Unfortunately Black Ops doesn't use PunkBuster, and VAC doesn't seem to be enough. So what is the preferred way to deal with players that are beyond any reasonable doubt cheaters (eg. you can clearly see in the kill cam, that they are using aimbot). 

I've tried to find some information on the Steam, but it seems they assume that VAC will detect the cheat automatically, and I don't see a clear path to actually report cheater that wasn't detected.