Nowadays, many programs are smart enough to bypass the usual text captcha and send you lots of spam everyday. In order to help solving the problem, you might want to try using an image captcha plugin, or something totally different and fun.
PlayThru is a set of simple, quick minigames that replaces the traditional text captcha. Basic account is free, it only takes a minute to install. For WordPress user, visit this page for installation instruction. If you are using Contact Form 7, a popular WordPress form plugin, the “Are You a Human” plugin will automatically detect it and allow you to include PlayThru in your CF7 form. Just add the “Are You a Human” element to the bottom of your form from within the CF7 setting page. PlayThru also supports Drupal, phpBB, vBulletin, Joomla, and many others.
Now the interesting part – you can also make money with PlayThru. PlayThru can be branded as an ad unit. According to their FAQ, the standard revenue sharing program is a 70/30 split, where publishers get 30% of the ad revenue. Once your account has reached a $200 threshold, you will be able to request a check. If you prefer to turn off branded games, you can upgrade your free account to a paid plan. More features and options are available to you. You can even create your own custom game for your website as part of their Enterprise plan. For more info, please visit Are You a Human.