Abstract
Many financial institutions have deployed CAPTCHAs to protect their e-banking systems from automated attacks. In addition to traditional CAPTCHAs for login, CAPTCHAs are also used to prevent malicious manipulation of e-banking transactions by automated Man-in-the-Middle (MitM) attackers. Despite serious financial risks, security of e-banking CAPTCHAs is largely unexplored. In this paper, we report the first comprehensive study on e-banking CAPTCHAs deployed around the world. A new set of image processing and pattern recognition techniques is proposed to break all e-banking CAPTCHA schemes that we have found over the Internet, including three e-banking CAPTCHA schemes for transaction verification and 41 schemes for login. These broken e-banking CAPTCHA schemes are used by a large number of financial institutions worldwide, which are serving hundreds of millions of e-banking customers. The success rate of our proposed attacks are either equal to or close to 100%. We also discuss possible enhancements to these e-banking CAPTCHA schemes and show some essential difficulties of designing e-banking CAPTCHAs that are both secure and usable.