The first self-propagating computer worm to infect a significant part of the early Internet in 1988 was the Morris worm.
Released on 2 November 1988, the Morris worm was created by Cornell University graduate student Robert Tappan Morris. It targeted Unix systems and exploited weaknesses or configuration issues involving services including sendmail, finger, and rsh. A programming mistake caused the worm to reinfect some computers repeatedly, consuming resources and slowing or disabling systems.
The worm did not destroy files in the way many later viruses did, but it spread widely enough to affect a substantial portion of the Internet then in existence. Morris was later convicted under the Computer Fraud and Abuse Act, becoming the first person convicted under that U.S. law.
The Morris worm helped establish computer-worm outbreaks as a major security concern. It is different from a virus because a worm can spread across networks without needing to attach itself to a host file or rely on a user to copy an infected program.