Precious digital content are subject to illegal copying. Digital rights management systems and digital watermarking are two common approaches to digital content protection with their limitations. In this paper, we propose a peer-to-peer approach to collaborative copy detection as a second line of defense for content protection. Collectively, a set of Web spiders forms a virtual team of "Web police" which continuously monitors the Web for potential candidates of illegal copies. Preliminary experimental results show the potential of the proposed approach.