Hello Everybody
among outgoing access via UDP port and to a DNS on port 53, there are conducted by AvastSvc.exe to the IP 209.95.34.40 (hostname = slc81-009.ff.avast.com)
Should I allow this outgoing access?
Best regards
Yes since it is needed for avast.
Thank you very much Eddy.
I come back!! 
after a little thinking time, I wonder if other outgoing access blocked by ZoneAlarm might also involve Avast. But then how do you know which ones? IP addresses are not explicit. I will not ask all these addresses one by one. It would be good Avast informs us.
What is the best solution?
Regards
The best solution is learning how things are working.
ZA is not just a firewall anymore and is known to conflict with other av’s.
I suggest you remove ZA and use a hardware firewall.
Many people don’t know it, but they often already have one.
What they call a modem (mostly issued by their ISP) is a multi function device.
e.g modem, router, firewall in one box.
If you want to use a software firewall, you can use the one build into Windows.
That is, if you have Windows 7 or later.
Prior versions only checked incoming traffic and not outgoing.
What you told me is very interesting. 
I’ll investigate further.
Thank you so much Eddy.