Breaking Visual CAPTCHAs with Naive Pattern Recognition Algorithms. - Jeff Yan; Ahmad Salah El Ahmad (ACSAC, 2007)

A low-cost attack on a Microsoft captcha. - Jeff Yan; Ahmad Salah El Ahmad (CCS, 2008)

Usability of CAPTCHAs or usability issues in CAPTCHA design. - Jeff Yan; Ahmad Salah El Ahmad (SOUPS, 2008)

CAPTCHA Security: A Case Study. - Jeff Yan; Ahmad Salah El Ahmad (IEEE Secur. Priv., 2009)

The robustness of a new CAPTCHA. - Ahmad Salah El Ahmad; Jeff Yan; Lindsay F. Marshall (EUROSEC, 2010)

Captcha Robustness: A Security Engineering Perspective. - J. Yan; Ahmad Salah El Ahmad (Computer, 2011)

CAPTCHA Design: Color, Usability, and Security. - Ahmad Salah El Ahmad; Jeff Yan; Wai-Yin Ng (IEEE Internet Comput., 2012)

The robustness of text CAPTCHAs. - Ahmad Salah El Ahmad (2012)