[Dean C]

Well if they do launch an attack on "yah" forum, there's little you can do really other than block them from spamming their URL with replacement variables. You can moderate new user registrations, but you could potentially end up blocking good, new members.

Also a patient spammer will always get around your filters for blocking their URL. for example if you block example.com they will come and spam saying example dot com, or e x a m p l e . c o m (remove the spaces) etc..