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- Breaking a Visual CAPTCHA by Greg Mori and Jitendra Malik
- Using AI to beat CAPTCHA and post comment spam by Casey Chestnut
- Pretend We're Not a Turing Computer but a Human Antagonist by Samuel HOCEVAR
- http://www.theregister.co.uk/2008/04/14/msn_captcha_breaking/
DDoS Attacks
- Using Graphic Turing Tests To Counter Automated DDoS Attacks Against Web Servers by William G. Morein Angelos Stavrou y Debra L. Cook
Angelos D. Keromytis Vishal Misra Dan Rubensteiny
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