I'm really sorry to hear about this problem Teo. I just started a forum for all my web sites so I haven't had any experience yet with this sort of thing and I hope I never do... although that might be kinda nieve..... anyway I have a friend that has helped me with my sites and he runs a forum too, we started getting rude posts like that too at his forum..... I asked him what he did to get rid of them. Here is what he said about it.......
He
probably couldn't block their ip because they just constantly switch
them. His best bet is to probably go into his database and find one of
the bad posts. Then look and see what it says for member id or name for
that post. Then he can go to his user table and find that name and
delete it. This seemed to work for us. Sorry, that probably is all
foreign but it's the only thing I know he could do.