Computer Viruses
A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. However, the term "virus" is commonly use
d, albeit erroneously, to refer to many different types of malware programs. The original virus may modify the copies, or the copies may modify themselves, as occurs in a metamorphic virus. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD, or USB drive. Meanwhile viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with computer worms and Trojan horses. A worm can spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a file that appears harmless. Both worms and Trojans will cause harm to computers when executed.
Most personal computers are now connected to the Internet and to local area networks, facilitating the spread of malicious code. Today's viruses may also take advantage of network services such as the World Wide Web, e-mail, Instant Messaging and file sharing systems to spread, blurring the line between viruses and worms. Furthermore, some sources use an alternative terminology in which a virus is any form of self-replicating malware.
Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply replicate themselves and perhaps make their presence known by presenting text, video, or audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.
History ::
The Creeper virus was first detected on ARPANET, the forerunner of the Internet in the early 1970s.It propagated via the TENEX operating system and could make use of any connected modem to dial out to remote computers and infect them. It would display the message "I'M THE CREEPER : CATCH ME IF YOU CAN.". It is rumored that the Reaper program, which appeared shortly after and sought out copies of the Creeper and deleted them, may have been written by the creator of the Creeper in a fit of regret.
A program called "Rother J" is commonly credited with being the first computer virus to appear "in the wild" — that is, outside the single computer or lab where it was created, but that claim is false. See the Timeline of notable computer viruses and worms for other earlier viruses. It was however the first virus to infect computers "in the home". Written in 1982 by Richard Skrenta, it attached itself to the Apple DOS 3.3 operating system and spread by floppy disk. This virus was originally a joke, created by a high school student and put onto a game. The disk could only be used 49 times. The game was set to play, but release the virus on the 50th time of starting the game. Only this time, instead of playing the game, it would change to a blank screen that read a message about the virus named Elk Cloner. The message that showed up on the screen is as follows:"Elk Cloner: The program with a personality It will get on all your disksIt will infiltrate your chipsYes it's Cloner!It will stick to you like glueIt will modify RAM tooSend in the Cloner!"
The computer would then be infected.
The first PC virus in the wild was a boot sector virus called (c)Brain[3], created in 1986 by the Farooq Alvi Brothers, operating out of Lahore, Pakistan. The brothers reportedly created the virus to deter pirated copies of software they had written. However, analysts have claimed that the Ashar virus, a variant of Brain, possibly predated it based on code within the virus.
Before computer networks became widespread, most viruses spread on removable media, particularly floppy disks. In the early days of the personal computer, many users regularly exchanged information and programs on floppies. Some viruses spread by infecting programs stored on these disks, while others installed themselves into the disk boot sector, ensuring that they would be run when the user booted the computer from the disk.
Traditional computer viruses emerged in the 1980s, driven by the spread of personal computers and the resultant increase in BBS and modem use, and software sharing. Bulletin board driven software sharing contributed directly to the spread of Trojan horse programs, and viruses were written to infect popularly traded software. Shareware and bootleg software were equally common vectors for viruses on BBS's. Within the "pirate scene" of hobbyists trading illicit copies of retail software, traders in a hurry to obtain the latest applications and games were easy targets for viruses.
Since the mid-1990s, macro viruses have become common. Most of these viruses are written in the scripting languages for Microsoft programs such as Word and Excel. These viruses spread in Microsoft Office by infecting documents and spreadsheets. Since Word and Excel were also available for Mac OS, most of these viruses were able to spread on Macintosh computers as well. Most of these viruses did not have the ability to send infected e-mail. Those viruses which did spread through e-mail took advantage of the Microsoft Outlook COM interface.
Macro viruses pose unique problems for detection software. For example, some versions of Microsoft Word allowed macros to replicate themselves with additional blank lines. The virus behaved identically but would be misidentified as a new virus. In another example, if two macro viruses simultaneously infect a document, the combination of the two, if also self-replicating, can appear as a "mating" of the two and would likely be detected as a virus unique from the "parents".
A virus may also send a web address link as an instant message to all the contacts on an infected machine. If the recipient, thinking the link is from a friend (a trusted source) follows the link to the website, the virus hosted at the site may be able to infect this new computer and continue propagating.
d, albeit erroneously, to refer to many different types of malware programs. The original virus may modify the copies, or the copies may modify themselves, as occurs in a metamorphic virus. A virus can only spread from one computer to another when its host is taken to the uninfected computer, for instance by a user sending it over a network or the Internet, or by carrying it on a removable medium such as a floppy disk, CD, or USB drive. Meanwhile viruses can spread to other computers by infecting files on a network file system or a file system that is accessed by another computer. Viruses are sometimes confused with computer worms and Trojan horses. A worm can spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a file that appears harmless. Both worms and Trojans will cause harm to computers when executed.Most personal computers are now connected to the Internet and to local area networks, facilitating the spread of malicious code. Today's viruses may also take advantage of network services such as the World Wide Web, e-mail, Instant Messaging and file sharing systems to spread, blurring the line between viruses and worms. Furthermore, some sources use an alternative terminology in which a virus is any form of self-replicating malware.
Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Others are not designed to do any damage, but simply replicate themselves and perhaps make their presence known by presenting text, video, or audio messages. Even these benign viruses can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes. In addition, many viruses are bug-ridden, and these bugs may lead to system crashes and data loss.
History ::
The Creeper virus was first detected on ARPANET, the forerunner of the Internet in the early 1970s.It propagated via the TENEX operating system and could make use of any connected modem to dial out to remote computers and infect them. It would display the message "I'M THE CREEPER : CATCH ME IF YOU CAN.". It is rumored that the Reaper program, which appeared shortly after and sought out copies of the Creeper and deleted them, may have been written by the creator of the Creeper in a fit of regret.
A program called "Rother J" is commonly credited with being the first computer virus to appear "in the wild" — that is, outside the single computer or lab where it was created, but that claim is false. See the Timeline of notable computer viruses and worms for other earlier viruses. It was however the first virus to infect computers "in the home". Written in 1982 by Richard Skrenta, it attached itself to the Apple DOS 3.3 operating system and spread by floppy disk. This virus was originally a joke, created by a high school student and put onto a game. The disk could only be used 49 times. The game was set to play, but release the virus on the 50th time of starting the game. Only this time, instead of playing the game, it would change to a blank screen that read a message about the virus named Elk Cloner. The message that showed up on the screen is as follows:"Elk Cloner: The program with a personality It will get on all your disksIt will infiltrate your chipsYes it's Cloner!It will stick to you like glueIt will modify RAM tooSend in the Cloner!"
The computer would then be infected.
The first PC virus in the wild was a boot sector virus called (c)Brain[3], created in 1986 by the Farooq Alvi Brothers, operating out of Lahore, Pakistan. The brothers reportedly created the virus to deter pirated copies of software they had written. However, analysts have claimed that the Ashar virus, a variant of Brain, possibly predated it based on code within the virus.
Before computer networks became widespread, most viruses spread on removable media, particularly floppy disks. In the early days of the personal computer, many users regularly exchanged information and programs on floppies. Some viruses spread by infecting programs stored on these disks, while others installed themselves into the disk boot sector, ensuring that they would be run when the user booted the computer from the disk.
Traditional computer viruses emerged in the 1980s, driven by the spread of personal computers and the resultant increase in BBS and modem use, and software sharing. Bulletin board driven software sharing contributed directly to the spread of Trojan horse programs, and viruses were written to infect popularly traded software. Shareware and bootleg software were equally common vectors for viruses on BBS's. Within the "pirate scene" of hobbyists trading illicit copies of retail software, traders in a hurry to obtain the latest applications and games were easy targets for viruses.
Since the mid-1990s, macro viruses have become common. Most of these viruses are written in the scripting languages for Microsoft programs such as Word and Excel. These viruses spread in Microsoft Office by infecting documents and spreadsheets. Since Word and Excel were also available for Mac OS, most of these viruses were able to spread on Macintosh computers as well. Most of these viruses did not have the ability to send infected e-mail. Those viruses which did spread through e-mail took advantage of the Microsoft Outlook COM interface.
Macro viruses pose unique problems for detection software. For example, some versions of Microsoft Word allowed macros to replicate themselves with additional blank lines. The virus behaved identically but would be misidentified as a new virus. In another example, if two macro viruses simultaneously infect a document, the combination of the two, if also self-replicating, can appear as a "mating" of the two and would likely be detected as a virus unique from the "parents".
A virus may also send a web address link as an instant message to all the contacts on an infected machine. If the recipient, thinking the link is from a friend (a trusted source) follows the link to the website, the virus hosted at the site may be able to infect this new computer and continue propagating.
The newest species of the virus family is the cross-site scripting virus.The virus emerged from research and was academically demonstrated in 2005. This virus utilizes cross-site scripting vulnerabilities to propagate. Since 2005 there have been multiple instances of the cross-site scripting viruses in the wild, most notable sites affected have been MySpace and Yahoo.
In order to replicate itself, a virus must be permitted to execute code and write to memory. For this reason, many viruses attach themselves to executable files that may be part of legitimate programs. If a user tries to start an infected program, the virus' code may be executed first. Viruses can be divided into two types, on the basis of their behavior when they are executed. Nonresident viruses immediately search for other hosts that can be infected, infect these targets, and finally transfer control to the application program they infected. Resident viruses do not search for hosts when they are started. Instead, a resident virus loads itself into memory on execution and transfers control to the host program. The virus stays active in the background and infects new hosts when those files are accessed by other programs or the operating system itself.
Nonresident viruses:
Nonresident viruses can be thought of as consisting of a finder module and a replication module. The finder module is responsible for finding new files to infect. For each new executable file the finder module encounters, it calls the replication module to infect that file.
Resident viruses
Resident viruses contain a replication module that is similar to the one that is employed by nonresident viruses. However, this module is not called by a finder module. Instead, the virus loads the replication module into memory when it is executed and ensures that
this module is executed each time the operating system is called to perform a certain operation. For example, the replication module can be called each time the operating system executes a file. In this case, the virus infects every suitable program that is executed on the computer.
Resident viruses are sometimes subdivided into a category of fast infectors and a category of slow infectors. Fast infectors are designed to infect as many files as possible. For instance, a fast infector can infect every potential host file that is accessed. This poses a special problem to anti-virus software, since a virus scanner will access every potential host file on a computer when it performs a system-wide scan. If the virus scanner fails to notice that such a virus is present in memory, the virus can "piggy-back" on the virus scanner and in this way infect all files that are scanned. Fast infectors rely on their fast infection rate to spread. The disadvantage of this method is that infecting many files may make detection more likely, because the virus may slow down a computer or perform many suspicious actions that can be noticed by anti-virus software. Slow infectors, on the other hand, are designed to infect hosts infrequently. For instance, some slow infectors only infect files when they are copied. Slow infectors are designed to avoid detection by limiting their actions: they are less likely to slow down a computer noticeably, and will at most infrequently trigger anti-virus software that detects suspicious behavior by programs. The slow infector approach does not seem very successful, however.
In order to replicate itself, a virus must be permitted to execute code and write to memory. For this reason, many viruses attach themselves to executable files that may be part of legitimate programs. If a user tries to start an infected program, the virus' code may be executed first. Viruses can be divided into two types, on the basis of their behavior when they are executed. Nonresident viruses immediately search for other hosts that can be infected, infect these targets, and finally transfer control to the application program they infected. Resident viruses do not search for hosts when they are started. Instead, a resident virus loads itself into memory on execution and transfers control to the host program. The virus stays active in the background and infects new hosts when those files are accessed by other programs or the operating system itself.
Nonresident viruses:
Nonresident viruses can be thought of as consisting of a finder module and a replication module. The finder module is responsible for finding new files to infect. For each new executable file the finder module encounters, it calls the replication module to infect that file.
Resident viruses
Resident viruses contain a replication module that is similar to the one that is employed by nonresident viruses. However, this module is not called by a finder module. Instead, the virus loads the replication module into memory when it is executed and ensures that
this module is executed each time the operating system is called to perform a certain operation. For example, the replication module can be called each time the operating system executes a file. In this case, the virus infects every suitable program that is executed on the computer.
Resident viruses are sometimes subdivided into a category of fast infectors and a category of slow infectors. Fast infectors are designed to infect as many files as possible. For instance, a fast infector can infect every potential host file that is accessed. This poses a special problem to anti-virus software, since a virus scanner will access every potential host file on a computer when it performs a system-wide scan. If the virus scanner fails to notice that such a virus is present in memory, the virus can "piggy-back" on the virus scanner and in this way infect all files that are scanned. Fast infectors rely on their fast infection rate to spread. The disadvantage of this method is that infecting many files may make detection more likely, because the virus may slow down a computer or perform many suspicious actions that can be noticed by anti-virus software. Slow infectors, on the other hand, are designed to infect hosts infrequently. For instance, some slow infectors only infect files when they are copied. Slow infectors are designed to avoid detection by limiting their actions: they are less likely to slow down a computer noticeably, and will at most infrequently trigger anti-virus software that detects suspicious behavior by programs. The slow infector approach does not seem very successful, however.
Vectors and hosts 
::
Viruses have targeted various types of transmission media or hosts. This list is not exhaustive:
Binary executable files (such as COM files and EXE files in MS-DOS, Portable Executable files in Microsoft Windows, and ELF files in Linux)
Volume Boot Records of floppy disks and hard disk partitions
The master boot record (MBR) of a hard disk
General-purpose script files (such as batch files in MS-DOS and Microsoft Windows, VBScript files, and shell script files on Unix-like platforms).
Application-specific script files (such as Telix-scripts)
Documents that can contain macros (such as Microsoft Word documents, Microsoft Excel spreadsheets, AmiPro documents, and Microsoft Access database files)
Cross-site scripting vulnerabilities in web applications
Arbitrary computer files. An exploitable buffer overflow, format string, race condition or other exploitable bug in a program which reads the file could be used to trigger the execution of code hidden within it. Most bugs of this type can be made more difficult to exploit in computer architectures with protection features such as an execute disable bit and/or address space layout randomization.
PDFs, like HTML, may link to malicious code.
It is worth noting that some virus authors have written an .EXE extension on the end of .PNG (for example), hoping that users would stop at the trusted file type without noticing that the computer would start with the final type of file. (Many operating systems hide the extensions of known file types by default, so for example a filename ending in ".png.exe" would be shown ending in ".png".) See Trojan horse (computing).
Methods to avoid detection
In order to avoid detection by users, some viruses employ different kinds of deception. Some old viruses, especially on the MS-DOS platform, make sure that the "last modified" date of a host file stays the same when the file is infected by the virus. This approach does not fool anti-virus software, however, especially that which maintains and dates Cyclic redundancy check on file changes.
Some viruses can infect files without increasing their sizes or damaging the files. They accomplish this by overwriting unused areas of executable files. These are called cavity viruses. For example the CIH virus, or Chernobyl Virus, infects Portable Executable files. Because those files had many empty gaps, the virus, which was 1 KB in length, did not add to the size of the file.
::Viruses have targeted various types of transmission media or hosts. This list is not exhaustive:
Binary executable files (such as COM files and EXE files in MS-DOS, Portable Executable files in Microsoft Windows, and ELF files in Linux)
Volume Boot Records of floppy disks and hard disk partitions
The master boot record (MBR) of a hard disk
General-purpose script files (such as batch files in MS-DOS and Microsoft Windows, VBScript files, and shell script files on Unix-like platforms).
Application-specific script files (such as Telix-scripts)
Documents that can contain macros (such as Microsoft Word documents, Microsoft Excel spreadsheets, AmiPro documents, and Microsoft Access database files)
Cross-site scripting vulnerabilities in web applications
Arbitrary computer files. An exploitable buffer overflow, format string, race condition or other exploitable bug in a program which reads the file could be used to trigger the execution of code hidden within it. Most bugs of this type can be made more difficult to exploit in computer architectures with protection features such as an execute disable bit and/or address space layout randomization.
PDFs, like HTML, may link to malicious code.
It is worth noting that some virus authors have written an .EXE extension on the end of .PNG (for example), hoping that users would stop at the trusted file type without noticing that the computer would start with the final type of file. (Many operating systems hide the extensions of known file types by default, so for example a filename ending in ".png.exe" would be shown ending in ".png".) See Trojan horse (computing).
Methods to avoid detection
In order to avoid detection by users, some viruses employ different kinds of deception. Some old viruses, especially on the MS-DOS platform, make sure that the "last modified" date of a host file stays the same when the file is infected by the virus. This approach does not fool anti-virus software, however, especially that which maintains and dates Cyclic redundancy check on file changes.
Some viruses try to avoid detection by killing the tasks associated with antivirus software before it can detect them.
As computers and operating systems grow larger and more complex, old hiding techniques need to be updated or replaced. Defending a computer against viruses may demand that a file system migrate towards detailed and explicit permission for every kind of file access.
Avoiding bait files and other undesirable hosts
A virus needs to infect hosts in order to spread further. In some cases, it might be a bad idea to infect a host program. For example, many anti-virus programs perform an integrity check of their own code. Infecting such programs will therefore increase the likelihood that the virus is detected. For this reason, some viruses are programmed not to infect programs that are known to be part of anti-virus software. Another type of host that viruses sometimes avoid is bait files. Bait files (or goat files) are files that are specially created by anti-virus software, or by anti-virus professionals themselves, to be infected by a virus. These files can be created for various reasons, all of which are related to the detection of the virus:
Anti-virus professionals can use bait files to take a sample of a virus (i.e. a copy of a program file that is infected by the virus). It is more practical to store and exchange a small, infected bait file, than to exchange a large application program that has been infected by the virus.
Anti-virus professionals can use bait files to study the behavior of a virus and evaluate detection methods. This is especially useful when the virus is polymorphic. In this case, the virus can be made to infect a large number of bait files. The infected files can be used to test whether a virus scanner detects all versions of the virus.
Some anti-virus software employs bait files that are accessed regularly. When these files are modified, the anti-virus software warns the user that a virus is probably active on the system.
Since bait files are used to detect the virus, or to make detection possible, a virus can benefit from not infecting them. Viruses typically do this by avoiding suspicious programs, such as small program files or programs that contain certain patterns of 'garbage instructions'.
A related strategy to make baiting difficult is sparse infection. Sometimes, sparse infectors do not infect a host file that would be a suitable candidate for infection in other circumstances. For example, a virus can decide on a random basis whether to infect a file or not, or a virus can only infect host files on particular days of the week.
Stealth :
Some viruses try to trick anti-virus software by intercepting its requests to the operating system. A virus can hide itself by intercepting the anti-virus software’s request to read the file and passing the request to the virus, instead of the OS. The virus can then return an uninfected version of the file to the anti-virus software, so that it seems that the file is "clean". Modern anti-virus software employs various techniques to counter stealth mechanisms of viruses. The only completely reliable method to avoid stealth is to boot from a medium that is known to be clean.
Self-modification
Most modern antivirus programs try to find virus-patterns inside ordinary programs by scanning them for so-called virus signatures. A signature is a characteristic byte-pattern that is part of a certain virus or family of viruses. If a virus scanner finds such a pattern in a file, it notifies the user that the file is infected. The user can then delete, or (in some cases) "clean" or "heal" the infected file. Some viruses employ techniques that make detection by means of signatures difficult but probably not impossible. These viruses modify their code on each infection. That is, each infected file contains a different variant of the virus.
Encryption with a variable key
A more advanced method is the use of simple encryption to encipher the virus. In this case, the virus consists of a small decrypting module and an encrypted copy of the virus code. If the virus is encrypted with a different key for each infected file, the only part of the virus that remains constant is the decrypting module, which would (for example) be appended to the end. In this case, a virus scanner cannot directly detect the virus using signatures, but it can still detect the decrypting module, which still makes indirect detection of the virus possible. Since these would be symmetric keys, stored on the infected host, it is in fact entirely possible to decrypt the final virus, but that probably isn't required, since self-modifying code is such a rarity that it may be reason for virus scanners to at least flag the file as suspicious.
An old, but compact, encryption involves XORing each byte in a virus with a constant, so that the exclusive-or operation had only to be repeated for decryption. It is suspicious code that modifies itself, so the code to do the encryption/decryption may be part of the signature in many virus definitions.
Polymorphic code
Polymorphic code was the first technique that posed a serious threat to virus scanners. Just like regular encrypted viruses, a polymorphic virus infects files with an encrypted copy of itself, which is decoded by a decryption module. In the case of polymorphic viruses however, this decryption module is also modified on each infection. A well-written polymorphic virus therefore has no parts which remain identical between infections, making it very difficult to detect directly using signatures. Anti-virus software can detect it by decrypting the viruses using an emulator, or by statistical pattern analysis of the encrypted virus body. To enable polymorphic code, the virus has to have a polymorphic engine (also called mutating engine or mutation engine) somewhere in its encrypted body. See Polymorphic code for technical detail on how such engines operate.
Some viruses employ polymorphic code in a way that constrains the mutation rate of the virus significantly. For example, a virus can be programmed to mutate only slightly over time, or it can be programmed to refrain from mutating when it infects a file on a computer that already contains copies of the virus. The advantage of using such slow polymorphic code is that it makes it more difficult for anti-virus professionals to obtain representative samples of the virus, because bait files that are infected in one run will typically contain identical or similar samples of the virus. This will make it more likely that the detection by the virus scanner will be unreliable, and that some instances of the virus may be able to avoid detection.
Metamorphic code
To avoid being detected by emulation, some viruses rewrite themselves completely each time they are to infect new executables. Viruses that use this technique are said to be metamorphic. To enable metamorphism, a metamorphic engine is needed. A metamorphic virus is usually very large and complex. For example, W32/Simile consisted of over 14000 lines of Assembly language code, 90% of it is part of the metamorphic engine.
Vulnerability and countermeasures
The vulnerability of operating systems to viruses
Just as genetic diversity in a population decreases the chance of a single disease wiping out a population, the diversity of software systems on a network similarly limits the destructive potential of viruses.
This became a particular concern in the 1990s, when Microsoft gained market dominance in desktop operating systems and office suites. The users of Microsoft software (especially networking software such as Microsoft Outlook and Internet Explorer) are especially vulnerable to the spread of viruses. Microsoft software is targeted by virus writers due to their desktop dominance, and is often criticized for including many errors and holes for virus writers to exploit. Integrated applications (such as Microsoft Office) and applications with scripting languages with access to the file system (for example Visual Basic Script (VBS), and applications with networking features) are also particularly vulnerable.
Although Windows is by far the most popular operating system for virus writers, some viruses also exist on other platforms. Any operating system that allows third-party programs to run can theoretically run viruses. Some operating systems are less secure than others. Unix-based OS's (and NTFS-aware applications on Windows NT based platforms) only allow their users to run executables within their protected space in their own directories.
An Internet based research revealed that there were cases when people willingly pressed a particular button to download a virus. A security firm F-Secure ran a half year advertising campaign on Google AdWords which said "Is your PC virus-free? Get it infected here!". The result was 409 clicks.
As of 2006, there are relatively few security exploits targeting Mac OS X (with a Unix-based file system and kernel). The number of viruses for the older Apple operating systems, known as Mac OS Classic, varies greatly from source to source, with Apple stating that there are only four known viruses, and independent sources stating there are as many as 63 viruses. It is safe to say that Macs are less likely to be targeted because of low market share and thus a Mac-specific virus could only infect a small proportion of computers (making the effort less desirable). Virus vulnerability between Macs and Windows is a chief selling point, one that Apple uses in their Get a Mac advertising.That said, Macs have also had security issues just as Microsoft Windows has, though none have ever been fully taken advantage of successfully in the wild.
Windows and Unix have similar scripting abilities, but while Unix natively blocks normal users from having access to make changes to the operating system environment, older copies of Windows such as Windows 95 and 98 do not. In 1997, when a virus for Linux was released – known as "Bliss" – leading antivirus vendors issued warnings that Unix-like systems could fall prey to viruses just like Windows. The Bliss virus may be considered characteristic of viruses – as opposed to worms – on Unix systems. Bliss requires that the user run it explicitly (so it is a trojan), and it can only infect programs that the user has the access to modify. Unlike Windows users, most Unix users do not log in as an administrator user except to install or configure software; as a result, even if a user ran the virus, it could not harm their operating system. The Bliss virus never became widespread, and remains chiefly a research curiosity. Its creator later posted the source code to Usenet, allowing researchers to see how it worked.
The role of software development
Because software is often designed with security features to prevent unauthorized use of system resources, many viruses must exploit software bugs in a system or application to spread. Software development strategies that produce large numbers of bugs will generally also produce potential exploits.
Anti-virus software and other preventive measures
Many users install anti-virus software that can detect and eliminate known viruses after the computer downloads or runs the executable. There are two common methods that an anti-virus software application uses to detect viruses. The first, and by far the most common method of virus detection is using a list of virus signature definitions. This works by examining the content of the computer's memory (its RAM, and boot sectors) and the files stored on fixed or removable drives (hard drives, floppy drives), and comparing those files against a database of known virus "signatures". The disadvantage of this detection method is that users are only protected from viruses that pre-date their last virus definition update. The second method is to use a heuristic algorithm to find viruses based on common behaviors. This method has the ability to detect viruses that anti-virus security firms have yet to create a signature for.
Some anti-virus programs are able to scan opened files in addition to sent and received e-mails 'on the fly' in a similar manner. This practice is known as "on-access scanning." Anti-virus software does not change the underlying capability of host software to transmit viruses. Users must update their software regularly to patch security holes. Anti-virus software also needs to be regularly updated in order to prevent the latest threats.
One may also prevent the damage done by viruses by making regular backups of data (and the Operating Systems) on different media, that are either kept unconnected to the system (most of the time), read-only or not accessible for other reasons, such as using different file systems. This way, if data is lost through a virus, one can start again using the backup (which should preferably be recent). If a backup session on optical media like CD and DVD is closed, it becomes read-only and can no longer be affected by a virus. Likewise, an Operating System on a bootable can be used to start the computer if the installed Operating Systems become unusable. Another method is to use different Operating Systems on different file systems. A virus is not likely to affect both. Data backups can also be put on different file systems. For example, Linux requires specific software to write to NTFS partitions, so if one does not install such software and uses a separate installation of MS Windows to make the backups on an NTFS partition, the backup should remain safe from any Linux viruses. Likewise, MS Windows can not read file systems like ext3, so if one normally uses MS Windows, the backups can be made on an ext3 partition using a Linux installation.
Recovery methods::Once a computer has been compromised by a virus, it is usually unsafe to continue using the same computer without completely reinstalling the operating system. However, there are a number of recovery options that exist after a computer has a virus. These actions depend on severity of the type of Virus.
Virus removal
One possibility on Windows XP and Vista is a tool known as System Restore, which restores the registry and critical system files to a previous checkpoint. Often a virus will cause a system to hang, and a subsequent hard reboot will render a system restore point from the same day corrupt. Restore points from previous days should work provided the virus is not designed to corrupt the restore files. Some viruses, however, disable system restore and other important tools such as Task Manager and Command Prompt. An example of a virus that does this is CiaDoor.
Administrators have the option to disable such tools from limited users for various reasons. The virus modifies the registry to do the same, except, when the Administrator is controlling the computer, it blocks all users from accessing the tools. When an infected tool activates it gives the message "Task Manager has been disabled by your administrator.", even if the user trying to open the program is the administrator.
If your system is a Microsoft product and you have your 20 digit registration number, you can go to the Microsoft web site, and they will do a free scan and most likely remove any known virus such as Trojan win32.murlo.
Operating system reinstallation
Reinstalling the operating system is another approach to virus removal. It involves simply reformatting the OS partition and installing the OS from its original media, or imaging the partition with a clean backup image (taken with Ghost or Acronis for example).
This method has the benefits of being simple to do, can be faster than running multiple anti-virus scans, and is guaranteed to remove any malware. Downsides include having to reinstall all other software as well as the operating system. User data can be backed up by booting off of a LiveCD or putting the hard drive into another computer and booting from the other computer's operating system
yamaha YFZ-R15
Biking just got hotter with the new Yamaha YZF-R15. Japan’s global bike giant Yamaha is rolling out the brand new sports motorcycle YZF-R15 for India motorcycling enthusiasts.
The YZF-R15 will be the first motorcycle in India with six gears after the old Yamaha RD 350. The engine is a liquid-cooled, four-stroke single cylinder four-valve fuel injected engine. Liquid cooling on the YZF R15 is a first for motorcycles in India. The 150cc engine produces 16 bhp. A lot of people would not be all that happy with that 150 cc specification of the YZF-R15. However, the 16 bhp and 6 gears would keep a lot of wannabe racers satisfied.
In India, Yamaha Motor Pvt Ltd’s stylish 150 cc high-end bike will take on the market segment so far ruled by Hero Honda’s Karizma, Bajaj Pulsar 220 DTS-FI and TVS Apache RTR.
How would it fare on the road against the Karizma? Initial guesses are that this 150cc crotch rocket would beat the Karizma in acceleration stakes. Top speeds are another issue altogether. However, we will have to wait for the initial test rides of the YZF-R15 to come in to have any clarity at all on this.
Yamaha India believes that the new model would kick start a new experience altogether for Yamaha enthusiasts.The model is being tipped as one of the most technologically advanced bikes in India. Yamaha in India is aggressively promoting YZF-R15, which will come sporting a price tag of close to Rs 100,000, and is targeting a sale of 25,000 units between now and December.
The pricing is a surprise. It was believed, post Auto-Expo 2008, that this motorcycle is likely to be priced quite a bit above Rs 1 lakh when it hits the roads. Yamaha has taken care of that; psychologically, that rs 1 lakh marke is a killer and might have ruined its chances in India.
The YZF-R15 motorcycle, looks-wise, takes after the Yamaha R1 superbike. The motorcycle is available in two colours, racing blue and black. This is also India’s first motorcycle with a full-fairing in front - lookswise, we can safely call it the best in the market.
Positioning it properly for the Indian market, Yamaha hopes for a re-emergence in the country’s bike mart after a slew of commuter bikes which the company ahs been churning out in the last decade after the iconic Yamaha RX 100.
As part of the launch, the company has also unveiled a series of events with test rides and is happy with the response. Yamaha Motor India Pvt Ltd today it plans to invest about Rs 800 crore in the next three years for product development, capacity expansion and marketing initiatives.
The YZF-R15 will be the first motorcycle in India with six gears after the old Yamaha RD 350. The engine is a liquid-cooled, four-stroke single cylinder four-valve fuel injected engine. Liquid cooling on the YZF R15 is a first for motorcycles in India. The 150cc engine produces 16 bhp. A lot of people would not be all that happy with that 150 cc specification of the YZF-R15. However, the 16 bhp and 6 gears would keep a lot of wannabe racers satisfied.
In India, Yamaha Motor Pvt Ltd’s stylish 150 cc high-end bike will take on the market segment so far ruled by Hero Honda’s Karizma, Bajaj Pulsar 220 DTS-FI and TVS Apache RTR.
How would it fare on the road against the Karizma? Initial guesses are that this 150cc crotch rocket would beat the Karizma in acceleration stakes. Top speeds are another issue altogether. However, we will have to wait for the initial test rides of the YZF-R15 to come in to have any clarity at all on this.
Yamaha India believes that the new model would kick start a new experience altogether for Yamaha enthusiasts.The model is being tipped as one of the most technologically advanced bikes in India. Yamaha in India is aggressively promoting YZF-R15, which will come sporting a price tag of close to Rs 100,000, and is targeting a sale of 25,000 units between now and December.
The pricing is a surprise. It was believed, post Auto-Expo 2008, that this motorcycle is likely to be priced quite a bit above Rs 1 lakh when it hits the roads. Yamaha has taken care of that; psychologically, that rs 1 lakh marke is a killer and might have ruined its chances in India.
The YZF-R15 motorcycle, looks-wise, takes after the Yamaha R1 superbike. The motorcycle is available in two colours, racing blue and black. This is also India’s first motorcycle with a full-fairing in front - lookswise, we can safely call it the best in the market.
Positioning it properly for the Indian market, Yamaha hopes for a re-emergence in the country’s bike mart after a slew of commuter bikes which the company ahs been churning out in the last decade after the iconic Yamaha RX 100.
As part of the launch, the company has also unveiled a series of events with test rides and is happy with the response. Yamaha Motor India Pvt Ltd today it plans to invest about Rs 800 crore in the next three years for product development, capacity expansion and marketing initiatives.
2008 chevrolet eqinox spots and pre launch news
The Chevy Equinox gets more powerful engine and better styling for 2008
GM’s new sport version of the 2008 Chevrolet Equinox is all set to hit the tarmac. Automajor General Motors Corp this week lifted the wraps off its compact Equinox sport utility vehicle and said that it would roll out the beauty by next summer.
Equipped with a more powerful engine and six-speed automatic transmission, larger wheels and some cosmetic features, the 2008 Chevrolet Equinox has been designed to give itself a more aggressive look. Auto enthusiasts may recall that the original Chevrolet Equinox had hit the showrooms in mid-2004 with not much hype. However, GM had earned much goodwill due to the vehicle. For 2008, the ride height has been lowered, stabilizer bars added and it gets a 140 mph top speed.
The 2008 Chevy Equinox is seen as competing with the Honda RAV4 and Mazda CX7 compact SUVs. It will also face the challenges posed by BMW's X3, Ford Escape and Jeep Liberty.
Analysts believe that though the SUV features may not bring in much cash inflow, GM might gain in terms of an image boost through the Equinox. The company has said that the version will deliver 263-horsepower performance, compared with the 185-horsepower of the traditional Equinox, and hit the 0-60 mph benchmark in seven seconds.
Price is still a secret with Chevrolet; but the vehicle will be available for the public in Q3 2007.
GM’s new sport version of the 2008 Chevrolet Equinox is all set to hit the tarmac. Automajor General Motors Corp this week lifted the wraps off its compact Equinox sport utility vehicle and said that it would roll out the beauty by next summer.
Equipped with a more powerful engine and six-speed automatic transmission, larger wheels and some cosmetic features, the 2008 Chevrolet Equinox has been designed to give itself a more aggressive look. Auto enthusiasts may recall that the original Chevrolet Equinox had hit the showrooms in mid-2004 with not much hype. However, GM had earned much goodwill due to the vehicle. For 2008, the ride height has been lowered, stabilizer bars added and it gets a 140 mph top speed.
The 2008 Chevy Equinox is seen as competing with the Honda RAV4 and Mazda CX7 compact SUVs. It will also face the challenges posed by BMW's X3, Ford Escape and Jeep Liberty.
Analysts believe that though the SUV features may not bring in much cash inflow, GM might gain in terms of an image boost through the Equinox. The company has said that the version will deliver 263-horsepower performance, compared with the 185-horsepower of the traditional Equinox, and hit the 0-60 mph benchmark in seven seconds.
Price is still a secret with Chevrolet; but the vehicle will be available for the public in Q3 2007.
hyundai tucson in india
Hyundai Motor is bringing the Hyundai Tucson to India . After the failure of the hyped-up Hyundai Terracan, the new compact SUV will be offered here as part of Hyundai's global rollout of Tucson (pronounced `Tuesawn'). Two variants are likely. Expect price tags between Rs 12 and Rs 15 lakh.
Hyundai Tucson in India will initially sport a 2000-cc DOHC 4-cylinder engine. There will be a continuously variable valve timing mechanism. A CRDi engine is also likely later, as a 2.7-litre V6 engine.Hyundai Motor India believes that there is a market for the Tucson in India. The other SUvs currently in India include Ford Endeavour, Honda CR-V, Mahindra Scorpio, Tata Safari, Toyota Land Cruiser Prado, Mitsubishi Pajero and Nissan X-Trail.
The Hyundai Tucson was first shown at the Chicago Auto Show in February 2004. Its design, user-friendly features, compact exterior dimensions, interiors and technology have attracted rave reviews. Overseas, the Hyundai Tucson is positioned against Toyota RAV4, Pontiac Vibe, Mitsubishi Outlander and Suzuki Reno. None of these models are available in India yet.The Hyundai Tucson is built on the Elantra sedan’s front-wheel-drive platform. The Tucson GL, abroad, is equipped with a 2.0-liter inline four cylinder with variable valve timing, tuned here to make about 140 horsepower and 136 lb.-ft. of torque. The 2005 Hyundai Tucson’s optional 4WD system is Borg-Warner’s Electronic InterActive Torque Management design that can route up to 99 percent of the power to the front wheels. Up to half of the engine’s power can be transferred rearward as road conditions and wheel slippage demand. A 4WD Lock feature allows the driver to lock the system for a steady 50/50 split, but there is no low gear for serious off-roading.
Hyundai Tucson in India will initially sport a 2000-cc DOHC 4-cylinder engine. There will be a continuously variable valve timing mechanism. A CRDi engine is also likely later, as a 2.7-litre V6 engine.Hyundai Motor India believes that there is a market for the Tucson in India. The other SUvs currently in India include Ford Endeavour, Honda CR-V, Mahindra Scorpio, Tata Safari, Toyota Land Cruiser Prado, Mitsubishi Pajero and Nissan X-Trail.
The Hyundai Tucson was first shown at the Chicago Auto Show in February 2004. Its design, user-friendly features, compact exterior dimensions, interiors and technology have attracted rave reviews. Overseas, the Hyundai Tucson is positioned against Toyota RAV4, Pontiac Vibe, Mitsubishi Outlander and Suzuki Reno. None of these models are available in India yet.The Hyundai Tucson is built on the Elantra sedan’s front-wheel-drive platform. The Tucson GL, abroad, is equipped with a 2.0-liter inline four cylinder with variable valve timing, tuned here to make about 140 horsepower and 136 lb.-ft. of torque. The 2005 Hyundai Tucson’s optional 4WD system is Borg-Warner’s Electronic InterActive Torque Management design that can route up to 99 percent of the power to the front wheels. Up to half of the engine’s power can be transferred rearward as road conditions and wheel slippage demand. A 4WD Lock feature allows the driver to lock the system for a steady 50/50 split, but there is no low gear for serious off-roading.