Around January 27, 2004, the MyDoom worm wreaked havoc on computer systems by leaving a back door—thereby permitting a cracker to gain access to computers infected by the worm at some later time. Several forms of the worm roamed the Internet in July 2004. Malicious programs related to Mydoom had been released under the names Doomjuice and Zindos. At the height of the release of these worms, Microsoft issued alerts urging users to take action to remove these worms and to keep their computers safe from other malicious intrusions by installing security features such as anti-virus software and firewalls.

See Also: Back or Trap Door; Intrusion; Worm.