Version 3.1.5 of the Akismet plugin for WordPress contains a critical security fix. Update your sites as soon as possible. We have no evidence that the bug has been exploited in the wild. The vulnerability is theoretically exploitable via comments, but to be as safe as possible, you should still upgrade immediately. The plugin is already blocking attempts during the comment-check API call even if you are not running the most recent version. To upgrade, visit the Updates page of your WordPress dashboard and follow the instructions.”]
Source: https://blog.akismet.com/2015/10/13/akismet-3-1-5-wordpress/