The open nature of peer-to-peer systems has played an important role in their growing popularity. The current file-sharing applications, for instance, have been widely used largely because they allow anyone to participate in them. This openness, however, brings up new issues because selfish, malicious, faulty, compromised, or resource-constrained peers may degrade a system. We explore the case for large-scale information dissemination through the design of the Trust-Aware Multicast (TAM) protocol. Nodes in TAM can exhibit uncooperative behavior such as delaying, discarding, modifying, replaying, and fabricating messages. While detecting such behaviors, TAM computes a level of trust for each node and adapts the underlying multicast tree according to trustworthiness of nodes, which leads to performance improvement in the system. The results from our simulation and PlanetLab experiments show that even with a significant portion of nodes being uncooperative, TAM is able to build a stable dissemination tree that provides lower message delay to well-behaved nodes.