When I started my computer this evening, avast asked about updating to 5.0.545, which I allowed.
Everything seemed fine, but it isn't.
I discovered soon that my mailclient Thunderbird wasn't getting any mails.
Soon I realized it was the avast-update. Previously avast and Thunderbird were getting along just fine. I have made absolutely no changes to my Thunderbird. Then I tried several changes in the avast-configuration concerning the mail-security which I had not touched before at all.
The only way I get my mails with Thunderbird is stopping the mail-checking of avast.
My Windows is Win 7 Home Premium 32bit.
I also checked the Win-Restoring (to yesterday) but Windows got messed up, no desktop showed up. Unsuccessful restoring in windows is a rare thing for and I'm doing that quite often. I don't know whether this has anything to do with avast as well. Anyway, undoing the restoring, having 5.0.545 again (with stopped mail-security) and my system is working again.
Please fix this Thunderbird-mail-problem.
Otherwise I'm a satisfied avast-free-user.