Standard Shield Sensitivity?

[softwareguy]

There are some files shown in Standard Shield settings that are not scanned. Is it possible that viruses hide in those files and infect my system? Should I have all files from the exclude list?

What about the scan on open extensions? Does Avast! try to detect the file type automatically and scans the file only if the file is infectable?

Lastly, Avast have default that it shall allow blocked actions in case of a screensaver running. Is that too big of a risk?

[igor]

There are some files shown in Standard Shield settings that are not scanned. Is it possible that viruses hide in those files and infect my system? Should I have all files from the exclude list?

No, virus cannot hide inside the exluded files.

What about the scan on open extensions? Does Avast! try to detect the file type automatically and scans the file only if the file is infectable?

I think it doesn't... the scanning is done just according to the extension here.

Lastly, Avast have default that it shall allow blocked actions in case of a screensaver running. Is that too big of a risk?

Well, this is the Behavior Blocker setting... which is a rather old feature, off by default. I don't see any big risk here...