FaH is sumed up well here FaH
It uses your spare CPU cycles to 'FOLD' you send and recieve WU's and i dont think anyone has access to your PC you just download and then upload an WU (Work Unit) When you are using your PC it uses up whats spare and when your not it uses up whats spare it never confilcts with programs that you are using. I fold in the background while gaming and it does't affect my gaming speeds. Just fold less during that period of time.
hope that helps