At the time the system was set to update the AES key on a daily basis, but it was found to only inconvenience illegal viewers little, and so the system was changed to update the key every 12 minutes. Since only TPS receivers could receive the key update, this was an effectively strategy. Crackers took one step further by managing to develop a system that successfully predicted key changes, but even though it would have been an effective hack, it wasn't possible to implement on most satellite receivers.