Prevent Spammers in your blog
From myhosting.com Wiki
Spammers search for web sites that allow anonymous comments to blog entries and fill them with their spam messages. To prevent this, you will need to set your blog scripts to allow comments only from registered users.
Also, many blogging scripts provide measures to detect multiple posts from same IP to prevent flooding. Contact the author of your blogging scripts for more information on how to fight spammers.
