Computer virus definition
A computer virus is a form of malicious software that piggybacks onto legitimate application code in order to spread and reproduce itself.
Like other types of malware, a virus is deployed by attackers to damage or take control of a computer. Its name comes from the method by which it infects its targets. A biological virus like HIV or the flu cannot reproduce on its own; it needs to hijack a cell to do that work for it, wreaking havoc on the infected organism in the process.