CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. CAPTCHAs are often used on websites that are attractive to spammers, such as forums, social networks, and commenting mechanisms. They do this by providing a word that is purposefully difficult to read, served on a noisy background. Because they are difficult, however, many website owners see them as a disruption to the flow of their user experience. However, they are often necessary to protecting the site from spam messages, which often do more damage.