Askimet is a spam filtering service for WordPress blogs. It filters out the worst of the comment spam leaving you free to be able to respond to the real comments out there. It checks every comment against their web service to see which are the real comments, and which are the spam ones that you don’t need to see.
Head over to the WordPress site to download the plugin if for some reason you don’t already have it (it comes as part of the WordPress package normally, but you may have uninstalled it) then head to the Askimet site to sign up. If you already have a WordPress.com account, you can use it here too. Click on the sign up for the personal link and adjust the slider to how much you want to pay for the plugin. If you don’t want to pay/are unable to, just slide the slider all the way to the left.
Once you’ve finished sign up, you’ll see the below screen which will explain how to add the code to your site – it’s pretty easy, just head to the settings page on the plugin and paste the API key in the box.
Askimet is free for personal blogs, and from $5/month for corporate ones.