Noun

(en noun)

Something that infects; that which causes infection.

*{{quote-journal, 2000, date=September 15, Robert Koenig, COMPUTER SCIENCE: Flushing Out Nasty Viruses in the Balkans, Science citation

, passage=That's when a rapidly proliferating virus from Israel dubbed Jerusalem bogged down computers around the world, and Brain--a "boot-sector infector " from Pakistan that hit MS-DOS systems--went on a rampage. }}