PS3-Sense writes: "Many people thought Sony didn't had a chance since the PS3's root key had been released. Some people were saying that this was the end of the PlayStation 3.
Nobody knew about it, but famous hacker SKFU has discovered this hidden feature in the PSN. The feature is meant to prevent people from playing downloaded games. We'll explain the feature.
When you buy a game you'll get a serial key with it, you can use this up to 5 times. This gives Sony a signal that you are authorised to play the game and that you have a legal copy of the game. The serial key only works with the same Blu-Ray disc with the same serial number. You can read more info about this on our website."