The Max Headroom pirating incident

From Wikipedia:

Max Headroom Pirating Incident occurred on Sunday November 22, 1987 and is an example of broadcast signal intrusion.

WGN
The first occurrence of the signal hijack occurred during WGN-TV's 9:00 News. During Bears Highlights in the Sports report the signal was interrupted by a video of a person wearing a Max Headroom mask in front of a swaying sheet of corrugated metal. There was no audio. The hijack was stopped after only 20 seconds when WGN switched transmission from the Sears Tower to the John Hancock Center. The incident left sports reporter Dan Roan flustered, who stated "Well, if you're wondering what happened… so am I."

WTTW
Later that night around 11:15pm during a broadcast of the Doctor Who episode Horror of Fang Rock on WTTW, the signal was hijacked by the same person. It was the same video that was broadcast during the WGN hijack, but this time there was audio. The person in the Max Headroom mask interrupted the broadcast, saying "He's a frickin nerd" before laughing and stating "Yeah I think I'm better than Chuck Swirsky!". The person continued to utter strange phrases including a Coke advertising slogan (Max Headroom was a Coke spokesperson at the time), humming the theme song to Clutch Cargo (pausing midway to say "I stole CBS"), he also states that he has, "made a giant masterpiece for all the greatest world's newspaper nerds" (WGN is an acronym for 'World's Greatest Newspaper'); before finally undressing below the waist and was spanked by an unknown person with a flyswatter before the masked person cut off his transmission. It was over in about 90 seconds. The pirate was never caught. WTTW, which maintains its transmitter atop the Sears Tower, found that its engineers were unable to stop the hijacker because at the time there were no engineers on duty at the Sears Tower. Also, the station's master control center was unable to contact its transmitting equipment remotely to switch the STL (Studio To Transmitter Link), unlike their counterparts at WGN-TV, who were able to thwart the intruder by switching their John Hancock Center transmitter STL remotely within seconds.

WTTW and WGN join HBO as victims of broadcast signal intrusion. There has not been an incident in America of this kind since. In January 2007 a broadcast hijack took place in Australia. The Max Headroom incident was reported on CBS Evening News.
(Wikipedia http://en.wikipedia.org/wiki/Max_Headroom_Pirating_Incident)