When I thought about asking this I was watching a StarCraft 2 replay, but I guess this can happen on any game that has spectators, in which secrecy is a major part of the game (like hiding your tech from your opponent in sc2).
How (if at all) are users prevented from spectacting a game and feeding information to a player via (for example) instant messaging? I'm guessing friends or clan members would do that.
Is this just ignored? Is it not a big problem in general?