http://en.wikipedia.org/wiki/GameGuard
nProtect GameGuard (sometimes called GG) is an anti-cheating software
Because of the way that GameGuard hooks into core system DLLs and interrupts[6], it is impossible (without hacking GameGuard and violating the TOS) to run games protected by GameGuard under Windows API Emulators, such as Wine under Unix-based operating systems[7]. The key issue being that GameGuard bypasses the OS safeguards in order to:
* Hide the game application process.
* Monitor the entire memory range.
* Terminate specific applications without the user consent (sometimes tries to disable Kernel hooks).
* Block specific calls to DirectX or the Windows API.
Don't try and compare this to Blizzard's Warden, which no longer scans out of game memory, doesn't kill process as it wishes, doesn't actively block API calls, nor does it imbed its self into your OS only to be removed via a reformat and reinstall.