CAPTCHA is a program that generates tests that require human users to submit answers for validation. These tests make it difficult for Internet scammers to flood a system with spam or harmful automated processes. The acronym "CAPTCHA" stands for Completely Automated Public Turing Test to Tell Computers and Humans Apart.
CAPTCHA is frequently used as a security checkpoint to deter Internet "bots" or program scripts designed to perform repetitive tasks autonomously.
Websites often use CAPTCHA to limit the number of attempts to enter a password. This method prevents the account holder from being locked out automatically while restricting a hacker's ability to test thousands of password combinations and gain access to personal information.