Avast must be intercepting attempts to contact a tracker that happens to be running on the same domain as a webpage that contains some content that Avast doesn't like.
There is no risk of Vuze downloading anything that might be considered a 'threat' when tracking a torrent - you could exclude Azureus.exe from being monitored by Avast probably (I don't know Avast configuration options I'm afraid) without risk.
It stopped showing the next day, I don't know if I finally deleted the torrent or something else happened.
It was the first time something like that happened in all the long years I've been torrenting (with Vuze)...
I can exclude Vuze from Avast real-time shields, but I think I'll leave it as it is, at least for now. I usually exclude the download folder, as it usually causes problems when downloading (disk errors and such). But then you must run a scan manually before opening suspicious files.
