What is a Computer Worm?

A computer worm differs from a computer virus in that a computer worm can run itself. A virus needs ahost program to run, and the virus code runs as part of the host program. A computer worm can spread without a host program, although some modern computer worms also use files to hide inside. The original computer worm was (perhaps accidentally) unleashed on the Internet by Robert Tappan Morris in1988. The Internet Worm used sendmail, fingerd, and rsh/rexec to spread itself across the Internet. The SQL Slammer Worm of 2003 used a vulnerability in Microsoft SQL Server 2000 to spread itself across the Internet. The Blaster Worm, also of 2003, used a vulnerability in Microsoft DCOM RPC to spread itself. The Melissa worm of 1999, the Sobig worms of 2003 and the Mydoom worm of2004 all spread through e-mail. These worms shared some features of a trojan horse,in that they spread by enticing a user to open an infected e-mail attachment.