Relegating Spambots

[Hyncharas]

I have an unusual question regarding spam that I'm interested in knowing how to fix. I've just installed Spam-O-Matic recently and it's working a treat, but there remains the question of what to do with all the spambot accounts still present on our servers. I suspect that if I delete these account, they will simply reappear and then I will have to ban them again... so what I want to do is have it so that "human" users are still in the Registered group, but any bots I place in the Banned section aren't recognised as registered themselves; so don't appear in the main forums' overall statistics.

I've asked VB.com and a friend who hosts another forum, but both say the technology isn't isn't in the code and directed me here. I'm not a programmer myself in PHP, so is there a plugin for this sort of thing?