Pingbacks allow you to notify other website owners that you have linked to their article on your website. Pingbacks were designed to solve some of the problems that people saw with trackbacks. Although there are some minor technical differences, a trackback is basically the same things as a pingback. Read more
These pingbacks can be used to send huge amounts of spam. Spammers use them to get their links posted on as many sites as possible. That is why they should be deactivated/cleaned if you do not use them.
You can either use our plugin Advanced Database Cleaner to clean-up these pingbacks or execute the following SQL code (which is used by the plugin) directly via your phpMyAdmin:
DELETE FROM comments WHERE comment_type = 'pingback'