On November 22, 1987, during the 9 O'Clock News sportscast, WGN-TV's analog broadcast signal was hijacked by an unknown person wearing a Max Headroom mask for approximately 25 seconds. This was only the first incident of that night involving the interruption of a television station's broadcast signal. Approximately two hours later, Chicago PBS station WTTW (channel 11) had its broadcast interrupted by the same person. WGN-TV's analog transmitter is atop the John Hancock Center and engineers were almost immediately able to thwart the video hacker by changing the studio-to-transmitter frequency, thus cutting the hacker off. Unfortunately for WTTW, its transmitter is atop Sears Tower and it was unable to stop the hacker before enduring almost two minutes of the hacker's interruption.