During a broadcast of the Dr. Who episode "Horror of Fang Rock" on WTTW Chicago Channel 11, on Sunday November 22nd, 1987, at around 11:15pm, a Video "Pirate" wearing a Max Headroom mask broke into the signal and transmitted one of the weirdest, unauthorized things ever to hit the Chicago airwaves.
The Max Headroom Pirating Incident
Maybe the greatest thing that's ever happened on TV (after SOY BOMB of course).