With avast! installed, it is possible to run a scan even when your computer is not being used and your screen-saver is running. A small window is displayed inside the screen-saver which informs you about the scanning progress, i.e. about the number of scanned files etc.
If you want avast! to scan your computer when the screen-saver is running, you need to locate the screen-saver option in your computer’s control panel and then select “avast! antivirus”.
To add this scan to the list of pre-defined scans on the Scan Now page, go to the program “Settings” and check the box “Show special scans in avast! user interface”. You will then be able to access and adjust the scan parameters as required.