[Digital Jedi]

Most spam modifications you use will block, or attempt to block, automated registrations and/or posts that come under specified parameters. Depending on your circumstance, you'll want something like this installed for it's convince. I use NoSpam! to prevent automated registrations.

But if your site was singled out by these nimrods who just like pushing people's buttons and seeing them freak out, your best bet, at least in my experience, is simple diligence. They get great pleasure out of seeing you and your members reaction to their nonsense. If you stay alert, delete they're posts and the accounts posing them as quick as you can and without comment, they'll tire quickly. There's no point in putting in all that effort to drive you crazy, if all you're going to do is undo everything they've done.