Breaking the clock face HIP

Web services designed for human users are being abused by computer programs (bots). The bots steal thousands of free, email accounts in a minute, participate in online polls to skew results, and irritate people in chat rooms. These real-world issues have recently generated a new research area called Human Interactive Proofs (HIP), whose goal is to defend web services from malicious attacks by differentiating bots from human users. For a HIP challenge to be effective, it needs to be both easy for human and robust against hots attacks. Recently, there is a new HIP design which is based on telling time from a clock face. This is a very innovative idea and quite easy for human to pass. However, its robustness to attacks needs verification. In this paper, we present an algorithm that can break the clock face HIP at 87.4%.