Thank you for your interesting reply, Tech.

I’m using the latest version of Avast 4.7.942. I downloaded it straight to a dvd before installing. That’s a method that I use all the time, when downloading software from the net. Then I’m scanning it with several antivirusprograms. Once cleared, I will install it on the computers where required.
So the problem is new because with earlier versions of Avast I never met this one. The firewall installed is from Windows Defender delivered with Vista Home Premium and was allready installed on the computer when I buyed it from Medion. As the other computers are not connected directly to the internet they are getting there updates via the Medion. In the case of Avast, I uninstall the old version and install the latest one. So there is not the problem.

Regards