|Matthew Broderick||David Lightman|
|Dabney Coleman||Dr. John McKittrick|
|Ally Sheedy||Jennifer Katherine Mack|
|John Wood||Dr. Stephen Falken|
|Barry Corbin||Gen. Jack Beringer|
|Juanin Clay||Pat Healy, McKittrick's assistant|
High school student David Lightman unwittingly hacks into a military supercomputer while searching for new video games. After starting a game of Global Thermonuclear War, Lightman leads the supercomputer to activate the nation's nuclear arsenal in response to his simulated threat as the Soviet Union. Once the clueless hacker comes to his senses, Lightman, with help from his girlfriend, must find a way to alert the authorities to stop the onset of World War III.