Most people we had to ban from our forums in the past are on dynamic IP ranges. So obviously it's pretty easy for them to sign up again using a different IP and email address. And we cannot ban an entire IP range of a huge provider. I was thinking it might be a good idea trying to track them using Flash cookies. Most people would just clear their browser cookies, get a new IP and email address and come back. If we are lucky they forget about the possibility to use Flash cookies to detect them. What do you think?