Computer program designed to copy itself into other programs, with the intention of causing mischief or damage. A virus will usually execute when it is loaded into a computer's memory. On execution, it instructs its host program to copy the viral code into any number of other programs and files stored in the computer. The corrupted programs may continue to perform their intended functions while also executing the virus's instructions, thus further propagating it. The infection may transfer itself to other computers through storage devices, computer networks, and on-line systems. A harmless virus may simply cause a cryptic message to appear when the computer is turned on; a more damaging virus can destroy valuable data. Antivirus software may be used to detect and remove viruses from a computer, but the software must be updated frequently for protection against new viruses.

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Microscopic, simple infectious agent that can multiply only in living cells of animals, plants, or bacteria. Viruses are much smaller than bacteria and consist of a single- or double-stranded nucleic acid (DNA or RNA) surrounded by a protein shell called a capsid; some viruses also have an outer envelope composed of lipids and proteins. They vary in shape. The two main classes are RNA viruses (see retrovirus) and DNA viruses. Outside of a living cell, a virus is an inactive particle, but within an appropriate host cell it becomes active, capable of taking over the cell's metabolic machinery for the production of new virus particles (virions). Some animal viruses produce latent infections, in which the virus persists in a quiet state, becoming periodically active in acute episodes, as in the case of the herpes simplex virus. An animal can respond to a viral infection in various ways, including fever, secretion of interferon, and attack by the immune system. Many human diseases, including influenza, the common cold, and AIDS, as well as many economically important plant and animal diseases, are caused by viruses. Successful vaccines have been developed to combat such viral diseases as measles, mumps, poliomyelitis, smallpox, and rubella. Drug therapy is generally not useful in controlling established viral infections, since drugs that inhibit viral development also inhibit the functions of the host cell. Seealso adenovirus; arbovirus; bacteriophage; picornavirus; plant virus; poxvirus.

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Minute infectious agent normally present in extremely small amounts in wild mice without causing obvious ill effects. It may induce cancerous tumours if grown in tissue culture and injected in large quantities into newborn mice or young hamsters, guinea pigs, and rabbits. It belongs to the Papovaviridae family of viruses.

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Any of various viruses that can cause plant disease (e.g., the tobacco mosaic virus). Plant viruses are economically important because many of them infect crop and ornamental plants. Numerous plant viruses are rodlike and can be extracted readily from plant tissue and crystallized. Most lack the fatty membrane found in many animal viruses, and all contain RNA. Plant viruses are transmitted in various ways, most importantly through insect bites, mainly by aphids and plant hoppers. Symptoms of virus infection include colour changes, dwarfing, and tissue distortion. The appearance of streaks of colour in certain tulips is caused by a virus. Seealso reovirus.

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Any of a group of viruses that cause warts and other harmless tumours in humans. More than 100 distinct types are known. Different types are responsible for warts of the hands, plantar warts (of the feet), and throat warts. Genital warts are caused by other types, which are spread by sexual intercourse. Some types of papillomaviruses that cause genital infections have been linked with various cancerous tumours, especially cervical cancers; their presence can be detected through a Pap smear.

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Virus of the Herpesviridae family that is the major cause of acute infectious mononucleosis. The virus, named for two of its discoverers, infects only salivary gland cells and one type of white blood cell. Saliva is the only bodily fluid that has been proved to contain infectious EBV particles. In less-developed nations, infection with EBV occurs in almost all children before the age of 5 and is not associated with recognizable symptoms. When EBV infection is delayed until the teen or early adult years, the body commonly responds differently, resulting in mononucleosis. Other, rarer disorders have also been linked with EBV, including certain cancers. There are no specific treatments for any form of EBV infection, and no vaccines have been developed.

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Microsoft Anti-Virus (MSAV) was an antivirus program introduced by Microsoft for its MS-DOS operating system. The program first appeared in MS-DOS version 6.0 and last appeared in version 6.22. The first version of the antivirus program was quite rudimentary, had no update facility (though a single update became available), and could only scan for about 1,000 viruses. Microsoft Anti-Virus for Windows (MWAV), included as part of the package, could be run under Windows 3.x.

History

Microsoft Anti-Virus was supplied by Central Point Software Inc. (later acquired by Symantec in 1994 and integrated into Symantec's Norton AntiVirus product) and was essentially a stripped down version of the Central Point Anti-Virus (CPAV) product which, in turn, Central Point Software Inc., had licensed from Carmel Software Engineering in Haifa, Israel. Carmel Software sold the product as Turbo Anti-Virus both domestically and abroad.

Microsoft Anti-Virus for Windows was also provided by Central Point Software. This product became noted as determining that the upgrade program of Windows 95 was detected as a computer virus, something which was embarrassing to Microsoft.

Features

Both the MS-DOS and Windows versions of the latest product had common features; the "Detect and Clean" strategy of Microsoft Anti-Virus could scan for and detect 1,234 distinct viruses. Other features included the detection of boot sector and trojan horse-type viruses which was the typical virus problem at the time.

The program also had an anti-stealth and checksum feature that could be used to detect any changes in normal files. This technology was intended to make up for the unavailability of regular update packages. Only one virus update was introduced since the original releases bringing the total protection to 2,371 viruses in 1996.

Windows XP and Vista

With the acquisition of GIANT Company Software and the release of Windows Defender (formerly Microsoft AntiSpyware), and the acquisition of RAV Antivirus from GeCAD Software, Microsoft has once again entered the antivirus market with:

• Windows Live OneCare (subscription program) for Windows XP and above
• Windows Live OneCare Safety Scanner, formerly Windows Live Safety Center (free web service) for Windows 2000 and above
• Windows Defender (free program) for XP, Server 2003, and is built into Windows Vista.

External links

• List of virus detected by MSAV