[from the obvious analogy with biological viruses,
via SF] A cracker program that searches out other programs and
`infects' them 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.
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 nice display hacks). Many nasty viruses, written by
particularly perversely minded crackers, do irreversible
damage, like nuking all the user's files.
In the 1990s, viruses have become a serious problem, especially
among Wintel and Macintosh users; the lack of security on these
machines enables viruses to spread easily, even infecting the
operating system (Unix machines, by contrast, are immune to such
attacks). The production of special anti-virus 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 not
only into techspeak but into also popular usage (where it is often
incorrectly used to denote a worm or even a Trojan horse). S
