There is a forum I visit and one of the people on there has a signature that seems to trigger a threat notification. It lists the site and then Url:Botnet
Have you considered that it can be a false positive? something to check first
@Bowdon
Whilst I have seen the same idiotic prats pulling stunts like this placing quasi code in text fields.
That said I haven't seen this make Avast alert in those that I have seen instances like this.
As for blocking it (or rather not scanning it), Url : Botnet isn't an actual address that you could possibly block in the Avast Web Shield. The only way it may be possible would be to add that forum to the web shield Exceptions.
Now you mention "It lists the site and then Url : Botnet" but you don't state any domain name (forum or external url) ?
If that is an external url to the forum, the last thing I would suggest would be to exclude that address from being scanned.
Personally I would suggest you report this to the actual forum effected by this.
What would help more is a screenshot of the Avast Alert, as we have no clue what the url/trigger is and whether you should add an exception or not.