It's the same on a few other sites I go on, one spammer keeps re-joining and sending the same PMs to people with the same nasty links in them. I mod on one of the sites where it's been a bad problem and we've had to temporarily ban some e-mail addresses from joining - usually googlemail or gmail ones. It sucks, I guess as some people are genuinely using those addresses to join, but there seems no other solution atm.