1945: Rear Admiral Grace Murray Hopper discovers a moth trapped between relays in a Navy computer. She calls it a “bug,” a term used since the late 19th century to refer to problems with electrical devices. Murray Hopper also coined the term “debugging” to describe efforts to fix computer problems.

1949: Hungarian scientist John von Neumann (1903-1957) describes, the theory of self-replicating programs, providing the theoretical foundation for computers that hold information in their “memory.”

1979: Engineers at Xerox Palo Alto Research Center discover the computer “worm,” a short program that affects, a network for idle processors. Designed to provide more efficient computer use, the worm is the ancestor of modern worms destructive computer viruses that alter or erase data on computers, often leaving files corrupted.

1983: University of Southern California doctoral candidate Fred Cohen coins the term “computer virus” to describe a computer program, that can “affect other computer programs by modifying them in such a way as to include a (possibly evolved) copy of itself.
1986: One of the first PC viruses ever created “The Brain,” is released by programmers in Pakistan.
1988: Twenty-three-year-old programmer Robert Morris unleashes a worm that invades ARPANET computers. The small program disables roughly 6,000 computers on the network by flooding their memory banks with copies of itself.

1994: Inexperienced e-mail users intentionally forward an e-mail warning people not to open any message with the phrase “Good Times” in the subject line. The message, warns of a virus with the power to erase a recipient’s hard drive, demonstrates the self-replicating power of e-mail virus hoaxes that continue to circulate in different forms today.

1995: Microsoft Corp. releases Windows 95. Anti-virus companies worry that the operating system will be resistant to viruses. Later in the year, however, evolved “macro” viruses appear that are able to corrupt the new Windows operating system.

1999: The infamous “Melissa” virus infects thousands of computers with alarming speed, causing an estimated $80 million damage and prompting record sales of anti-virus products. The virus starts a program, that sends copies of itself to the first 50 names listed in the recipient’s Outlook e-mail address book. It also infects Microsoft Word documents on the user’s hard drive, and mails them out through Outlook to the same 50 recipients.

2000: The “I Love You” virus infects millions of computers virtually overnight, using a method similar to the Melissa virus. The virus also sends passwords and usernames stored on infected computers back to the virus’s author. Authorities trace the virus to a young Filipino computer student who goes free because the Philippines has no laws against hacking and spreading computer viruses.

2001: The “Anna Kournikova” virus, promising digital pictures of the young tennis star, mails itself to every person listed in the victim’s Microsoft Outlook address book.

2001: In late May / early June 2001, there was a hoax concerning the “sulfnbk.exe” “virus”. Email went around the world telling people that on May 25 (or June 1) 2001 the “virus” would “activate”. People were told how to delete the file from their system. The email was in the form of a chain letter and told people to forward the letter to everyone they’d sent email in the past few months and warn them about this file

2001: The Code Red worm infects tens of thousands of systems running Microsoft Windows NT and Windows 2000 server software, causing an estimated $2 billion in damages. The worm is programmed to use the power of all infected machines against the White House Web site at a predetermined date.

2001: Debuting just days after the Sept. 11 attacks, the “Nimda” virus infects hundreds of thousands of computers around the world. The virus is considered one of the most sophisticated, with up to five methods of infecting systems and copying itself.

2002 : The “Klez” worm a bug that sends copies of itself to all of the e-mail addresses in the victim’s Microsoft Outlook directory - begins its march across the Web. The worm overwrites files and creates hidden copies of the originals. The worm also attempts to disable some common anti-virus products and has a payload that fills files with all zeroes. Variants of the Klez worm remain the most active on the Internet.
2003 : The “Slammer” worm infects hundreds of thousands of computers in less than three hours. The worm ever wreaks havoc on businesses worldwide, knocking cash machines offline and delaying airline flights. It holds the ranking as the fastest-spreading computer worm ever.

2004 : The “MyDoom” worm becomes the fastest-spreading e-mail worm as it causes headaches ,but very little damage. MyDoom uses “social engineering” or low- tech psychological tricks, to persuade people to open the e-mail attachment that contains the virus. It claims to be a notification, that an e-mail message sent earlier has failed, and prompts the user to open the attachment to see what the message text originally said.