Comment Runner is a free WordPress plugin to reduce or eliminate comment spam.
How Does Comment Runner Work?
Comment Runner checks WordPress comments for HTML hyperlinks. If one is found, the comment is placed in your comment-“trash” folder.
This technique is effective because it denies spammers what they’re after — an SEO advantage through hyperlinks and lead generation through email.
Additionally, Comment Runner hides the author-URL input box that’s visible by default in WordPress. In a perfect world, this would allow your readers to submit their blog (as a link) to a comment he/she submitted. Unfortunately, this is now abused by bots.
By hiding it (the author-URL input box), a “real” user can’t add content. So, if this plugin detects content in the input box, it can conclude with certainty that the message is spam and mark it as “trash.”