Recommended tools/techniques for monitoring for spam attacks on multi-site and shared servers
ether try the free mollom service or you can blacklist words before they get submitted. Another solution that does well is just use the disqus module to regulate your commenting. i have switched over to disqus completely. but its not seo friendly as its a js script call from what i remember. if you want seo capability best you blacklist words and links. say if someone posts a link it would throw an error. this would deter any link spammers as most bots posts links.