Source : WordNet®

phage
     n : a virus that is parasitic in bacteria; it uses the
         bacterium's machinery and energy to produce more phage
         until the bacterium is destroyed and phage is released to
         invade surrounding bacteria [syn: {bacteriophage}]

Source : Free On-Line Dictionary of Computing

phage
     
        A program that modifies other programs or databases in
        unauthorised ways; especially one that propagates a {virus} or
        {Trojan horse}.  See also {worm}, {mockingbird}.  The
        analogy, of course, is with phage viruses in biology.
     
        [{Jargon File}]