Its simple the Anti cheats have to use the same Strategies as the cheat writers. A good anti cheat needs to have full access to the operating system. either this will be Windows only or some Virtual Machine.
Best would be if the UT3 Engine would make it hard to access their code, however that is difficult, and its impossible to make it completely shut as long you have full control over your hard and software
only want to mention : Trusted Computing
Who told lately, most anti-cheat tools don't do more than anti-virus tools: Searching for signatures of known cheats.
And the real big problem is, you can earn money with cheats, but you can't with anti cheat tools.