A big problem for WordPress sites is spam in comments that are posted by bots or spammers. To reduce spam, there are WordPress plugins like Akismet, but one effective way in addition to captchas, or even limiting users who can comment, is the use of the Stop Spammer Registration plug-in. This plug-in actually compares comments, IP addresses to those on the StopForumSpam.com, Project Honeypot and BotScout sites and flags them as spam or valid.