Technically it is illegal due to modifying the game code which you're not allowed to do - yet I've never known anyone to get into trouble for legally owning the game and cracking it.
gamecopyworld doesn't host cracks anymore but will subtley guide you to a game fix site
I had to check this as they were always my first port of call after installing a game I'd bought, just looked and it appears to be business as usual thank god
Gamecopyworld have stopped hosting cracks for some games., but still have them for most of them. Annoyingly for some older games, e.g. Undying or Medal of Honor Allied Assault, using a no-CD crack is the only way to run them, in Vista.....