1. (virology) ultramicroscopic infectious agent that replicates itself only within cells of living hosts; many are pathogenic; a piece of nucleic acid (DNA or RNA) wrapped in a thin coat of protein
2. a harmful or corrupting agency;
"bigotry is a virus that must not be allowed to spread"
"the virus of jealousy is latent in everyone"
3. a software program capable of reproducing itself and usually capable of causing great harm to files or other programs on the same computer;
"a true virus cannot spread to another computer without human assistance"