A worm is a malware that is designed to propagate and spread across networks. Worms are known to propagate using one or several of different transmission vectors like email, IRC, network shares, instant messengers (IM), and peer-to-peer (P2P) networks.
Worms do not infect files, but may carry one or more payloads, such as computer security compromise and information theft.
Worms typically modify system settings to automatically start. Users may need to terminate worms before they can be deleted. Also, restoring affected systems may require procedures other than scanning with an antivirus program.