Hiddy WordPress Plugin is a captcha like system to prevent from spam comment and Based on Merlinox’s idea. The installation is really simple, just download the copressed file and explode it as it is (with it’s own folder) in the /wp-content/plugins folder. Then go to the manager and click on Activate link. This plugin will add a simple input text in the comments form, this text will be hidden with a stylesheet and the when a user post a comment it will check for the input and check if it is empty. So simple, so efficent.