1982 Elk Cloner affected programs for the Apple II computer, though the description of virus was not yet used.
1983 Researcher Fred Cohen uses the term computer virus for the first time in a research paper.
1986 The Brain virus was the first to attack systems running Microsoft's DOS.
1988 The Morris Internet worm is developed by a Cornell graduate student, the son of a government computer security expert. He inadvertently lets it loose and disables the Internet. It's also the year the first antivirus software is created.
1989 Stealth viruses begin to appear, so named because they use techniques to avoid detection.
1992 The Michelangelo virus, timed to the artist's 517th birthday, creates fears of widespread problems but turns out to be a mild attack.
1994 The Good Times virus is a hoax, but rumors about it float for a year.
1995 The first viruses to attack macro functions used to automate processes in Microsoft Word appear.
1996 The Boza virus is the first specifically targeted at the Microsoft Windows 95 operating system.
1997 The FBI's Law Enforcement Bulletin has an article on five computer viruses - all hoaxes mentioned in a joke e-mail. Included in the strains: the Clinton and Gingrich viruses.
1999 The Melissa outbreak combined elements of viruses and worms. It spread by e-mail, but also infected document files in thousands of computers.
1999 Distributed denial of service attacks begin, crippling major Web sites. To carry out the attacks, computers were hacked and had software secretly installed.
2000 The Love Bug, so named because of ILOVEYOU in the e-mail subject line, invades millions of computers and uses the Outlook e-mail program address book to send copies of itself to others. It also replaces photo and music files with copies of itself.
2001 The Code Red Worm takes control of infected computers to generate massive Internet traffic, blocking access to some sites.
2001 The Nimda worm strikes just a week after Sept. 11, packing multiple methods to infect machines.
2002 The Klez e-mail virus can be launched even if the user doesn't open the message.
2003 SoBig, Slammer and MSBlast are among a rash of viruses, worms and malware that spread quickly and break new ground in infecting machines.
2004 Trojan.Xombe and similar strains ratchet up "phishing" techniques to fool users into divulging personal information.
Compiled from Times files; "Malware: Fighting Malicious Code," by Ed Skoudis; Computer Knowledge; Discovery Channel Canada; and Security Focus.
