I'm running Windows 7 64-bit. Avast simply does not want to be stopped. Even SYSTEM does not kill it. I'm using these tools to run CMD as SYSTEM: http://reboot.pro/files/file/237-runassystem-and-runfromtoken/
See the following screenshot:
I even run CMD from the process token, and it still does not want to be terminated. So, how can I kill the damn thing?