Publish-subscribe is a communication paradigm that supports dynamic, many-to-many communications in a distributed environment. Content-based pub-sub systems are often implemented on a peer-to-peer infrastructure that enables information dissemination from information producers (publishers) to consumers (subscribers) through a subscription mechanism. In a wide-area pub-sub network, the pub-sub service must handle information dissemination across distinct authoritative domains, heterogeneous platforms and a large, dynamic population of publishers and subscribers. Such an environment raises serious security concerns. In this paper, we investigate the security issues and requirements that arise in an internet-scale content-based pub-sub system. We distinguish among those requirements that can be achieved with current technology and those that require innovative solutions.