There's no doubt that there are plenty of Cheaters and they have played undetected for a longtime if not since the beginning. The 'smart' Cheaters don't go to the freebie websites, download and install those hacks, but instead they seek boutique sites, programmers or write them their self. An AimBot doesn't require much in the way of coding to work and the Assist-AimBots are practically impossible to see unless someone also uses a Wall Hack.
Further, there are good players with good aim that don't cheat not to mention Clans and Parties (Pubstomp) to dominate a bunch of unsuspecting Random's all communicating with open mic's.