Or you could just BAN the user from the Control Panel » Member Management » Edit Profile > Permissions tab.
Banning the user with an expiration of "never," will block them from using that account again.
Also report those spammer user accounts to SFS. This will submit their IP and EMAIL addresses to the SFS service.
In the Control Panel » Registration Settings screen, confirm that you have enabled the following:
Enable Email Verification
Require A Unique Email Per Account
From reading through the rest of this thread, I can see that you're already on top of this horrible situation. You've put in to place a lot of the tools already written in to UBBT, and you've been further proactive in preventing it from getting out of hand.
Here is another took you can use, if you have access to your "htaccess" file.
http://www.ip2location.com/blockvisitorsbycountry.aspxI highly recommend that you read up on what it does, if you are not already aware.
And as you've mentioned earlier in your topic, IP addresses can easily be spoofed. So there's that, too. :/
