"Cheating is a superserious threat," says [Steam's lead engineer, John] Cook. "Cheating is more of a serious threat than piracy."
The company combats this with its own Valve Anti-Cheat System, which a user consents to install in the Steam subscriber agreement. Cook says the software gets around antivirus programs by handling all the operations that require administrator access to the user's machine.
So how important is preventing cheating? How much privacy are you willing to sacrifice in the interests of a level playing field?
Valve also looks for changes within the player’s computer processor’s memory, which might indicate that a cheat code is running.