:phage: n. A program that modifies other programs or databases in
unauthorized ways; esp. one that propagates a {virus} or
{Trojan horse}. See also {worm}, {mockingbird}. The
analogy, of course, is with phage viruses in biology.
-- The AI Hackers Dictionary
Trojan horse: [coined by MIT-hacker-turned-NSA-spook Dan Edwards]
n. A malicious, security-breaking program that is disguised as
something benign, such as a directory lister, archiver, game, or
(in one notorious 1990 case on the Mac) a program to find and
destroy viruses!...