CAPTCHA
Abstract
ABSTRACT
A CAPTCHA is a Turing test designed to distinguish between humans and automated scripts. These tests ensure that the user is a genuine person and not an automated script. CAPTCHAs can serve a variety of applications including but not limited to preventing: spam comments on blogs, automated fake registrations on website registration forms, automated voting in online polls, dictionary attacks on password systems, automated posting on forums and message boards, and automated usage of an online service beyond a specific threshold. Furthermore, under certain conditions CAPTCHAs can also be used to mitigate Denial of Service (DoS) attacks in combination with other security mechanisms. Since a large number of organizations and people rely on online services, DoS attacks and misuse of these services can have high negative impact and cause loss to the service provider. Therefore, measures against such attacks are important to ensure secure and reliable services. As a result, CAPTCHAs are widely used to protect online services such as email, web transactions, and mobile banking.
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