Here's a story that I heard from World of Warcraft. At the time, people only cared about the Ahn'Qiraj raid for the final boss. The raid itself took an eternity just to get there, and if the group wiped, that was a huge run back to the boss.
One guild found out a way to alter the game files to remove a floor under the first boss, as the final boss was just down there. Everyone who used this trick got a permanent ban.