WarGames

A 1983 science fiction film starring Matthew Broderick and Ally Sheedy in which a hacker manages to gain access to a top-secret military computer in control of the United States' arsenal of ICBMs. The teenager, unaware of the machine's real purpose, discovers what he believes to be a simulation game called "Global Thermonuclear War" and begins to "play". Unbeknownst to him, the computer sets in motion preparations for a real attack against the Soviet Union. With the aid of the machine's creator, disaster is narrowly averted when the hacker manages to teach the computer about the futility of war by getting it to play endless drawn games of tic-tac-toe against itself.

In part a cautionary tale about technology and the dangers of leaving machines in control of unleashing destruction (in an echo of the Doomsday device of Dr Strangelove, it was one of the first movies to deal with teenage hackers and their activities.