You simply cannot do all checks on all users at all times.
It is generally totally feasible to do SOME checks on all users all the time, and if those checks turn up something fishy, then increase the logging level for that account. Hell, you could even have human-initiated logging (Reporting of users).
Hell, you do not even need software to do this - a player gets reported via email, then an admin watches that player in a game, maybe even sends them messages ("Please respond to confirm you are actually at the keyboard")
So saying "We cannot solve this problem because it would impact performance for everyone" is a cheap cop-out.
Biting the hand that feeds IT
