Using the correct discussion settings on your WordPress site can help you reduce spam. You can also keep inappropriate words or sites from appearing on your posts comments section.
Comment spam can become a nuisance as your WordPress sites get more popular. If your WordPress sites are on a do follow list of blogs then you might notice even more comment spam. There are settings you can use to control how to handle all comments and one of the most useful is the comment blacklist section.
The discussion settings sub panel is found under Settings, Discussion. If you are getting a lot of spam and want to moderate all comments, as I currently do on this site, then check the E-mail me whenever – Anyone posts a comment and Before a comment appears – An administrator must always approve the comment . This will notify the WordPress sites administrator when all comments are posted.
As I mentioned above the Comment Blacklist is useful to mark comments as spam with any unwanted words in its content, name, URL or e-mail. You can also put the spammers IP address in the blacklist section. This is useful if you get habitual spam from the same source, just copy the information from the spam comment and paste it into the blacklist to mark all comments from the abuser as spam.
Read more about the Discussion Settings at the WordPress Codex.