Defense against Intrusion in a Live Streaming Multicast System Application-level multicast systems are vulnerable to attacks that impede nodes from receiving desired data. Live streaming protocols are especially susceptible to packet loss induced by malicious behavior. We describe SecureStream, an application-level live streaming system built using a pull-based architecture that results in improved tolerance of malicious behavior. SecureStream is implemented as a layer running over Fireflies, an intrusion-tolerant membership protocol. Our paper describes the SecureStream system and offers simulation and experimental results confirming its resilience to attack