Breaking Audio CAPTCHAs

CAP T C H A s are computer-generated tests that humans can pass but current computer systems cannot. CAP T C H A s provide a method for automatically distinguishing a human from a computer program, and therefore can protect Web services from abuse by so-called "bots." Most CAP T C H A s consist of distorted images, usually text, for which a user must provide some description. Unfortunately, visual CAP T C H A s limit access to the millions of visually impaired people using the Web. Audio CAP T C H A s were created to solve this accessibility issue; however, the security of audio CAP T C H A s was never formally tested.