Columbia University Telecom Italia SIP Communicator Peer-to-peer (P2P) networks offer higher robustness against failure, easier configuration and are generally more economical than their client-server counterparts. It has therefore become reasonable for resource consuming and typically centralized applications like Voice over IP (VoIP) and, in general, realtime communication to adapt and exploit the benefits of P2P. Such a migration needs to address a new set of P2P specific security problems. This document describes some of the known issues found in common P2P networks, analyzing the relevance of such issues and the applicability of existing solutions when using P2P architectures for realtime communication.