The Max Headroom Incident
This one is unexplained, in that nobody knows who did it or how they did it. On Nov. 22, 1989, a hacker managed to take over the frequencies of two Chicago-area TV stations. The first time, during a CBS newscast, technicians shut it down in 30 seconds. But the second attack, against a public TV station, lasted well over a minute. The PBS drama cut out and a man in a Max Headroom mask appeared, broadcasting a cryptic audio message, with lines like "your love is fading" and a hummed snippet of the theme song from the cartoon "Clutch Cargo" [source: Finley].
An Federal Communications Commission investigator said that whoever did it could have used simple gear, but had to have a sophisticated knowledge of broadcasting technology.