Hi Igor, thanks for your reply.
As for "doesn't work", I mean if I change the settings as described, Avast doesn't appear to detect the virus nor take any action. Avast only seems to detect and take action when set to "interactive".
To test it, I downloaded a copy of the harmless eicar virus, 'eicar.com', available at
www.eicar.org. Then I use right-mouse click to copy 'eicar.com' file to a new file (e.g. eicar2.com).
When set to the standard shield to Interactive (with or without 'silent'), Avast detects the virus and takes action.
However, if I change the settings as described above, then Avast doesn't detect the virus, and lets me copy and/or run the file without any messages or actions.
I'm using Avast Pro 4.1.319 and WinXP with all possible updates and patches applied.