It appears installing FAH is unnecessary, I was able to duplicate the behavior using this trivial program. Compile and run it and you will find that cmpro suddenly becomes very slow at scanning. (At least on x64 versions of Windows) Note that if you have multiple cores you will need to start one instance per core or set the affinity of both processes to the same CPU.

#include <Windows.h>

int main()
{
	SetPriorityClass(GetCurrentProcess(), IDLE_PRIORITY_CLASS);
	for(;;){}
}