CS has a concept of "trust factor" which groups people more likely to be cheating in the same game. If you ever queue with a friend with a low trust factor (which happens a lot if they're on a smurf account), there are cheaters in pretty much every game... seeing that many blatant cheaters has really made me think there must be a lot of smarter cheaters flying under the radar in regular games. It's basically impossible to tell whether someone is wallhacking or if they have really good game sense.