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ReCAPTCHA.net Now Vulnerable to Algorithmic Attack

Posted by timothy on from the bless-you! dept.

n3ond4x writes "reCAPTCHA.net algorithms have been developed to solve the current CAPTCHA at an efficacy of 30%. The algorithms were disclosed at DEFCON 18 over the weekend and have since been made available online. Also available is a video demonstration of random reCAPTCHA.net CAPTCHAs being subjected to the algorithms." There's probably an excellent Firefox plugin to render this page's color scheme more bearable. Note: the PowerPoint presentation linked opens fine in OpenOffice, and the video speaks for itself.

1 of 251 comments (clear)

  1. Re:far from it by hydrofix · · Score: 5, Informative

    Since both words need to be correct "solve the current CAPTCHA at an efficacy of 1%" would be closer to the truth.

    Actually, that is incorrect. The other word is already positively known by the OCR, and serves as a control, while the other is the one that the OCR could not read. It will of course only check the one that it knowns, and assumes the other one is then correct as well. So, if you get one of the words correct AND this is the same word that as their OCR identified correctly (which is very likely the case), then you pass, but most of the time (99%) give a bad answer for the harder, non-OCR word. Sadly, this leads to pollution of their database in the long run.