Purposes of worms

Many early communicable programs, including the Internet Worm and a number of MS-DOS viruses, were written as experiments or mischief generally intended to be harmless or merely annoying rather than to cause serious damage. Young programmers learning about viruses and the techniques used to write them might write one to prove that they can do it, or to see how far it could spread. As late as 1999, extensive viruses such as the Melissa virus appear to have been written chiefly as pranks.

A slightly more antagonistic intent can be found in programs designed to vandalize or cause data loss. Many DOS viruses, and the Windows Explore Zip worm, were designed to destroy files on a hard disk, or to corrupt the file system by writing junk data. Network-borne worms such as the 2001 Code Red worm or the Ramen worm fall into the same group. Designed to vandalize web pages, these worms may seem like the online equivalent to graffiti tagging, with the author's alias or similarity group appearing everywhere the worm goes.