If you run a system scan it's better to turn off your screen saver.
A little but very efficient and fast way is the program
QkSav2k 2.06 (Screensaver Control Powertoy) On contrary, I do not turn off the on-access scan. I understand what Artras posted but I will forget to turn it on after
If you let the screen saver start and the avast screen saver module in your screen saver, you will be scanning twice: system + screen saver and, if you want, the third will be on-access... Well, it's not necessary, time consuming and useless