Do not worry about these files… virus cannot make anything with them and from them… They are swap (temporary) files in constant changing. Scanning them can freeze the computer. Actually, sometime ago I tried this in XP and the computer freezed… GoBack saved my computer. Thanks God! 
No, these are the default avast configuration.
Let them like this. Do not change the settings if you are not sure.
If you want more security, try the ‘High’ sensitivity of the scanner.
Hope my experience help you to feel secure ;D