I feared the worst when my own site got a random comment attached to a very old post with the words "Nice Site!". As suspected, the poster's URL leads to a commercial porn site. Now I see the same spammer has hit Blogcritics. Looks like a lot of MT blogs have been hit. With just one spam post on my blog, I got off lightly.
Teresa Nielsen Hayden of Making Light, another victim, wishes a case of boils on the perpetrator. I'll add a severe case of piles to that. I'll leave it to Eric to suggest further unpleasant ailments.
This post on the Movable Type support forum suggests a drastic solution; renaming the legitimate MT Comments script, and replacing the original with a spider trap that adds the perp to the banned IP list in the HTACCESS file.
Meanwhile someone's done some detective work and identified the porn spammer as based in, you've guessed it, Florida. There's always the Traveller Imperial Navy solution; "Nuke the state from orbit, it's the only way to be sure!"
If you run a Movable Type blog, be sure to add the IP Address: 22.214.171.124 to your IP ban list.