There are plenty of options out there, of anti-cheat apps that run with the client app, scanning for known cheat programs and watching the process list for them. For an example, Lineage 2 uses one called hGuard/GameGuard, and has since like 2005. Not sure exactly how well it works, given the amount of botting that still went on there, but it's just an example. Another is WoW and Warden.