If I may jump in here, I haver had similar experiences. I have been running Avast for a while now, & have been having periodic crashes. Just after Christmas I started fresh with a new hard drive, new OS install etc. The crashes kept on happening. Saturday night, for no apparent reason, the computer re-booted, scanned the HD, repaired some damaged files, & then did it again 2 minutres later. The result is a 160 Gig of unreadable unrecognizable hard drive. I would up having to reformat & start afresh.
I am not using avast at this moment, however if you wish, I have a second computer I am trying to network. When I get it up & running I will run the same setup I had on my main box, with Avast & Sygate firewall, & see if I can duplicate the crashes.
I will keep you informed.
John