virus

n. [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 horse s. 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 hack s).
Many nasty viruses, written by particularly perversely minded cracker s, do
irreversible damage, like nuking all the user's files. In the 1990s, viruses
became a serious problem, especially among Windows 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.
See phage; compare back door; see also Unix conspiracy.