Hi everybody,
problem solved, avast does not connect to that adult site any more during the update process, also those ".vbs" files do not appear any more in the update messages.
During the boot-time scan avast found three viruses:
07/12/2009 01:42
Controllo di tutti i drives locali
File E:\System Volume Information\_restore{4845F5C9-A05A-47D7-9371-C4CB905DB49C}\RP56\A0054917.exe e infetto da Win32:Buttons [Joke], Spostato nel Cestino
File E:\System Volume Information\_restore{4845F5C9-A05A-47D7-9371-C4CB905DB49C}\RP56\A0054957.exe e infetto da Win32:Trojan-gen {Other}, Spostato nel Cestino
File E:\System Volume Information\_restore{4845F5C9-A05A-47D7-9371-C4CB905DB49C}\RP56\A0054975.exe e infetto da Win32:Trojan-gen {Other}, Spostato nel Cestino
Numero di cartelle cercate: 16536
Numero files controllati: 216771
Numero files infetti: 3
(sorry for the Italian messages. "Spostato nel cestino" means, literally, "Moved to the basket". Now I understand also that note about disabling system restore)
I've been able to update my hosts list using the dial-up connection, now I'm not so sure which step actually solved the problem... shall I edit the first post of this topic mentioning the steps I took? Which is the custom here about solved issues' threads?
Another question: into the avast recycled basket (or quarantine basket, I ignore its name in English), there are the three files reported above and also three system libraries: kernel32.dll, winsock.dll and wsock32.dll. All of them have been transferred to the basket at the end of the boot-time scan (at least it seems so, looking at their transfer times). Is it normal for such files to appear there?
By the way, thank you Tech for your explanation about proxy/firewall. In my mind I thought that the proxy could, at least, forbid connections to an eventual backdoor that could infect my system, that was what I meant with the word "safe". I'm going to set up a firewall asap, and I'll try to update my OS too.
Thanks again everybody, your help has been precious.
All the best,
Frank