Breaking the clock face HIP [Web services human interactive proofs]

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 bots 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. We present an algorithm that can break the clock face HIP at 87.4%.