Donde
Avast protects your computer while your using it, if a virus is opened or is doing something to your computer avast should pick it up without you having to scan.
But if you would like to stop this click the "A" ball in your taskbar (next to your system clock) and select "stop on access protection", this will effectivly leave it "dormant" and will wait in the taskbar (not in use or using any memory) as an quick/easy way to activate it again.
--lee