Now the meaning has changed to become something of a portmanteau term associated with the breaking into or harming of any kind of computer or telecommunications system.
Purists claim that those who break into computer systems should be properly called "crackers" and those targeting phones should be known as "phreaks".

1969 Arpanet. Arpanet, the forerunner of the internet, is founded. The first network has only four nodes.

1970s: Phone Phreaks and Cap'n Crunch: Phone hackers (phreaks) break into regional and international phone networks to make free calls. One phreak, John Draper (aka "Cap'n Crunch"), learns that a toy whistle given away inside Cap'n Crunch cereal generates a 2600-hertz signal, the same high-pitched tone that accesses AT&T's long-distance switching system.

Draper builds a "blue box" that, when used in conjunction with the whistle and sounded into a phone receiver, allows phreaks to make free calls.

Shortly thereafter, Esquire magazine publishes "Secrets of the Little Blue Box" with instructions for making a blue box, and wire fraud in the United States escalates. Among the perpetrators: college kids Steve Wozniak and Steve Jobs, future founders of Apple Computer, who launch a home industry making and selling blue boxes.

1971 Email Program. First e-mail program written by Ray Tomlinson and used on Arpanet which has now 64 nodes.

1972 Captain Crunch. John Draper, also known as Captain Crunch, finds that a toy whistle given away in the cereal with the same name could be used to mimic the 2600 hertz tones phone lines used to set up long distance calls.

1980: Hacker Message Boards and Groups
Phone phreaks begin to move into the realm of computer hacking, and the first electronic bulletin board systems (BBSs) spring up.

The precursor to Usenet newsgroups and e-mail, the boards -- with names such as "Sherwood Forest" and "Catch-22" -- become the venue of choice for phreaks and hackers to gossip, trade tips, and share stolen computer passwords and credit card numbers.

Hacking groups begin to form. Among the first are Legion of Doom in the United States, and Chaos Computer Club in Germany.

In October, Arpanet comes to a crashing halt thanks to the accidental distribution of a virus.

1983: Kids' Games
The Internet is formed when the Arpanet is split into military and civilian sections.

Wargames, a film that glamorises hacking, is released. Many hackers later claim it inspired them to start playing around with computers and networks.

The movie "War Games" introduces the public to hacking, and the legend of hackers as cyberheroes (and anti-heroes) is born. The film's main character, played by Matthew Broderick, attempts to crack into a video game manufacturer's computer to play a game, but instead breaks into the military's nuclear combat simulator computer.

The computer (codenamed WOPR, a pun on the military's real system called BURGR) misinterprets the hacker's request to play Global Thermonuclear War as an enemy missile launch. The break-in throws the military into high alert, or Def Con 1 (Defense Condition 1).

The same year, authorities arrest six teenagers known as the 414 gang (after the area code to which they are traced). During a nine-day spree, the gang breaks into some 60 computers, among them computers at the Los Alamos National Laboratory, which helps develop nuclear weapons.