Just saw this article on cheating in CoD , take a look its very interesting.
Notice there are no aimbots that work that this guy could find, so dont blame me next time I take your head off from one end of hte map to the other
The only two cheats I feel I have seen so far on COD are wallhacks and fullbright hacks. Both of which can be done at graphics driver level so are hard for COD to spot.
Some people moan about the KillCam, but its vital in keping this sort of thing under control. Most cheaters are just too stupid to mask their actions. You can see wallhack users tracking people behind walls etc.
I also have a demo I took of a COD player I was convinced was using a fullbright hack. This is harder to prove as he/she is either blessed with eyes that can spot a moving pixel and evaluate that its an enemy in 10ms. Or (as I think is likely) those 4 pixels were glowing bright green against the muted tones of the map. That game also showed the other tell-tale cheat effect; the player scored over twice what anyone else on the server did (and the server was not just full of old gits like me )
Was killing 3/4 of the enemy team each round, pulling of circus shots. Blindfolded. Like, htf did he know where to throw that nade?
Once is well played, second time is suspect, third and 15th time, it's blatantly cheating.