CAPTCHA Theory

• CAPTCHA.net

• How lazy cryptographers do AI By Luis von Ahn, Manuel Blum ,and John Langford

• CAPTCHA:Using Hard AI Problems For Security by Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford

• Mathematical Foundations for Understanding and Designing Conceptualizing Strategizing Control (CONSCS) Systems by Manuel Blum (PI), Avrim Blum (Co-PI), Lenore Blum (Co-PI), Steven Rudich (Co-PI),
  Research Assistants: Ryan Williams, Luis von Ahn

CAPTCHA tests

• Verifying the Presence of Humans:Three New CAPTCHAs by Neal R. Wagner
• A 3D captcha by Michael G. Kaplan

Accessibility

• Proposal for an Accessible Captcha
• Inaccessibility of Visually-Oriented Anti-Robot Tests by Matt May
• Dive Into Accessibility personas by Mark Pilgrim

Breaking

• 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

• Botz-4-Sale: Surviving Organized DDoS Attacks That MimicFlash Crowds by Srikanth Kandula Dina Katabi Matthias Jacob Arthur Berger
• MOVE: An End-to-End Solution To Network Denial of Service by Angelos Stavrou Angelos D. Keromytis Jason Nieh Vishal Misra Dan Rubenstein

Spam

• Fighting Spam May Be Easier Than You Think by Cynthia Dwork
• Securing Business's Front Door -Password, Token, and Biometric Authentication by Lawrence O'GormanAvaya