A CAPTCHA (an acronym for "Completely Automated Public Turing test to tell Computers and Humans Apart") is a type of challenge-response test used in computing to determine whether or not the user is human.

The reason websites have CAPTCHA is spam. The crazy letters are a way to check if the person registering or trying to comment is a real live human being as opposed to a computer program attempting to spam the site. 

The most up to date version of CAPTCHA is available on all DIY forms. If your form does not have this version, you can update it by taking the form live. This version requires that the user check a box that says "I'm not a robot" and may require the user to perform additional tasks to verify.

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Users won’t always get the extra verification tasks. This article does a nice job explaining why sometimes you just have to click a box and other times you have to click on some pictures based on a prompt.

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