[wikka-community] Any blacklist plugin?

[fishy]

Hi folks, I've got spams these days, and all the spammers use
xxx at mail.ru or xxx at list.ru as the email to register user (only
registered user can edit pages on my wiki). So if there're any
existing blacklist plugin, my life will be much easier. Is there any?

Or if not, I may start one. Any examples or clues on how to begin?

Thanks in advance.

-- 
regards,
fishy