[R@f]

I had similar problems on one of my SMF forums some years ago. To protect you from spam, you can either use a captcha system such as KeyCaptcha or Recaptcha, or use Akismet. I personally use KeyCaptcha and I'm very happy with it, not a single bot since I have it.

If you have an SMF forum, check this link for anti-spam modules : http://custom.simplemachines.org/mod...search;type=19