Not only that, you can create clones that can't be banned at all. It will fill up your server and all you can do is rehost. (Ban/kick/whatever and they will just rejoin).
Then there's also the "block" messages that can be spammed too, yes. Banning the IP won't work unless you block the IP via your firewall.
But then again, if only a proxy is used you're screwed anyway. I can perhaps try and get the packets with WPE :-/. There's a player searching for breaches inside JJ2+ to still be able to annoy people.

http://www.jazz2online.com/jcf/showp...70&postcount=1

Some screenshot of the actual clones, not that it will matter much.