Way to go cheating morons, you broke Call of Duty 4. A new exploit (which will not be detailed here; you can at least do some work if you want to cheat) has allowed a number of glitches to surface. Flying people and infinite ammo are breaking the multi-player aspects thanks to the exploit.
Infinity Ward is on the problem, which is affecting both the Xbox 360 and PS3 versions of the game, despite early reports being PS3 centric. Infitity Ward is taking the issue seriously, updating their Twitter account to let players know where they stand on getting this idiocy fixed. Hopefully bans are in order after this is all settled.