The difference between a virus and a worm
Viruses and worms are cousins in the malware world. Today it is common to find malware that includes the characteristics of both these once relatively distinct species. Although there is constant debate in the research world about what constitutes a virus vs. a worm, I like to use the following as a base-line: Virus -- a program that self-replicates. Worm -- a program that propagates without action from a user or program -- no host is required.