# Computer Virus

A type of malicious software that attaches itself to a legitimate program and spreads by infecting other files when run.

A **computer virus[↗](/computer-virus)** is a type of malware[↗](/malware) that attaches itself to a legitimate file or program and spreads by infecting other files or systems whenever the host program runs, similar to how a biological virus needs a host cell to replicate. Unlike a worm[↗](/worm), a virus generally needs some user action, like opening an infected file, to start spreading.

Once active, a virus can corrupt data, steal information, or turn a machine into a launching point for further attacks. Antivirus[↗](/antivirus) software detects viruses by recognizing known patterns in infected files and by watching for suspicious behavior from programs that try to modify other files without a clear reason.