Introduction 3 A Secure CAPTCHA Implementation 3 Breaching Client-Side Trust 4Hidden fields and client-side storage4Chosen CAPTCHA text attack5Arithmetic CAPTCHAs7 Server-Side Attacks 7CAPTCHA Rainbow Tables7 Attacking static CAPTCHA identifiers 7 Attacking dynamic CAPTCHA identifiers 8The chosen CAPTCHA identifier attack9CAPTCHA fixation10In-session CAPTCHA brute-forcing12CAPTCHA accumulation13 Attacking the Image 13OCR-assisted CAPTCHA brute-forcing13Testing CAPTCHAs with TesserCap14Writing custom CAPTCHA solvers15 Conclusion 16 About The Author 16 About Foundstone Professional Services