vi·rus    Audio Help   /ˈvaɪrəs/ Pronunciation Key - Show Spelled Pronunciation[vahy-ruhs] Pronunciation Key - Show IPA Pronunciation

–noun, plural -rus·es.

1.	an ultramicroscopic (20 to 300 nm in diameter), metabolically inert, infectious agent that replicates only within the cells of living hosts, mainly bacteria, plants, and animals: composed of an RNA or DNA core, a protein coat, and, in more complex types, a surrounding envelope.

2.	Informal. a viral disease.

3.	a corrupting influence on morals or the intellect; poison.

4.	a segment of self-replicating code planted illegally in a computer program, often to damage or shut down a system or network.

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[Origin: 1590–1600; < L vīrus slime, poison; akin to ooze²]

—Related forms

vi·rus·like, adjective

plur. viruses

Microorganisms consisting of DNA and RNA molecules wrapped in a protective coating of proteins. Viruses are the most primitive form of life. They depend on other living cells for their reproduction and growth. (See under “Medicine and Health.”)

Note: Viruses cause many diseases. (See viral infection.)

plur. viruses

A minute organism that consists of a core of nucleic acid surrounded by protein. Viruses, which are so small that a special kind of microscope is needed to view them, can grow and reproduce only inside living cells. (See under “Life Sciences.”)

See computer virus.

virus security
(By analogy with biological viruses, via SF) A program or piece of code written by a cracker that "infects" one or more other programs by embedding a copy of itself in them, so that they become Trojan horses. When these programs are executed, the embedded virus is executed too, thus propagating the "infection". This normally happens invisibly to the user.
A virus has an "engine" - code that enables it to propagate and optionally a "payload" - what it does apart from propagating. It needs a "host" - the particular hardware and software environment on which it can run and a "trigger" - the event that starts it running.
Unlike a worm, a virus cannot infect other computers without assistance. It is propagated by vectors such as humans trading programs with their friends (see SEX). The virus may do nothing but propagate itself and then allow the program to run normally. Usually, however, after propagating silently for a while, it starts doing things like writing "cute" messages on the terminal or playing strange tricks with the display (some viruses include display hacks). Viruses written by particularly antisocial crackers may do irreversible damage, like deleting files.
By the 1990s, viruses had become a serious problem, especially among IBM PC and Macintosh users (the lack of security on these machines enables viruses to spread easily, even infecting the operating system). The production of special antivirus software has become an industry, and a number of exaggerated media reports have caused outbreaks of near hysteria among users. Many lusers tend to blame *everything* that doesn't work as they had expected on virus attacks. Accordingly, this sense of "virus" has passed into popular usage where it is often incorrectly used for a worm or Trojan horse.
See boot virus, phage. Compare back door. See also Unix conspiracy.
[The Jargon File]
(2003-06-20)

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