What is the meaning of virus?

noun

• 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. (
• A harmful or corrupting agency.
  • usage: "bigotry is a virus that must not be allowed to spread"; "the virus of jealousy is latent in everyone"
• A software program capable of reproducing itself and usually capable of causing great harm to files or other programs on the same computer.
  • usage: "a true virus cannot spread to another computer without human assistance"
  • synonyms: computer virus