The problem is that the folder is variable as it will be in each new virus definitions folder that is the avast\defs[b]11072501[/b]\ bit (equates to 2011 July 25 2nd update of the day) and that may change around twice a day with new virus definitions.

I don’t use OA, so I have no idea how you would go about this, but you need to craft an exclusion something like d:\Program Files\AVAST Software\Avast\defs*\sf.bin the * being a wildcard that should cater for the changing folder name or exclude the defs folder and its contents, d:\Program Files\AVAST Software\Avast\defs*