http://en.wikipedia.org/wiki/1984_Rose_Bowl#Scoreboard_prank
They had to break in to the Rose Bowl stadium, design and build special boards to take over the scoreboard lights, and break back in to install the boards. The control of the board during the halftime break in the Rose Bowl game was done by RF link. This was in 1984, when hardware was much more finicky and expensive.
http://www.nytimes.com/1984/01/04/sports/sports-people-prank...
http://en.wikipedia.org/wiki/Great_Rose_Bowl_Hoax
They even made the first few compromised banners subtle enough that the crowd kept going with it until the finale where they wrote "CALTECH," an unmistakable prank.
A more detailed story is here: http://today.caltech.edu/today/story-display?story_id=11464