The best way to 100% block these kinds of registrations usually require some custom programming. My brother's website had the same problem when it was first opened, and the months that followed, but have since been 100% eliminated. From what I understand, he built what he called a signup gateway, that does all sorts of checks and balances, and adds the user to the database, then block registrations through the forum's signup page. If things get bad I can give the TGP's (is that the acronym you guys use for this place?) admin his email address, to share notes..