A virus that spreads by creating duplicates of itself on other drives, systems, or networks. A mass-mailing worm is one that requires a user's intervention to spread, (e.g., opening an attachment or executing a downloaded file). Unlike viruses, worms do not infect other files. Most of today's email viruses are worms. A self-propagating worm does not require user intervention to spread. Examples of self-propagating worms include Blaster, Sasser, and Conficker.