virus

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 have 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 anti-virus software
   has become an industry, and a number of exaggerated media reports
   have caused outbreaks of near hysteria among users; many
   {luser}s 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}).  See {phage}; compare {back door};
   see also {UNIX conspiracy}.