Improving Audio CAPTCHAs

CAPTCHAs are computer generated tests that humans can pass but current computer systems cannot. CAPTCHAs provide a method for automatically distinguishing a human from a computer program, and therefore can protect web services from bots. Most CAPTCHAs consist of distorted images, usually text, for which a user must provide some description. Unfortunately, visual CAPTCHAs limit access to the millions of visually impaired people using the web. Audio CAPTCHAs were created to solve this accessibility issue; however, the security of audio CAPTCHAs was never formally tested. We analyze the security of current audio CAPTCHAs, and provide a description and analysis of a new and improved audio CAPTCHA.