Build a powerful computer, it becomes self-aware and turns evil. We've seen this theme in many movies including 2001: A Space Odyssey, War Games and Terminator 3. Computer scientists as Frankensteins, building monsters they cannot control.
In 1982, Disney put together a TV special that tried to argue against the computers as monster theme. They could have used a better title than "Computers are People, Too!" and avoided pushing their new movie Tron about an evil computer.
Colossus did scare me as a kid but when I grew up I realized computers, as powerful as they get, don't become self-aware or inherently evil and they can always be rebooted or unplugged. Bad people can use computers in evil ways but computers themselves are just tools not the perpetrators.
I bring this up because of the new movie Stealth opening today in the States about a plane controlled by a computer that becomes self-aware and starts destroying stuff. Scaring a new generation about the evils of computer science.