Sahri,
You might be right.
Microsoft has now released 3 updates under KB915597. The latest one was released today (Aug 23, 2013).
I had 1 customer who was supposed to come in today with a similar problem (machine running very, very slow), calling me that all is fine now after he received the latest update as part of the KB article.
Next week, I will make sure the latest update to the KB is on the other 2 machines and see if Avast will run again.
Raoul.