Fighting Attacks in P2P Live Streaming. Simpler is Better P2P live streaming applications are becoming more popular each day. In contrast to the client-server model, the P2P approach overcomes problems such as system scalability and need for powerful resources in a single point. However, P2P networks may suffer from attacks and opportunistic behaviors. In this paper we present a decentralized reputation system to fight attacks in P2P livestreaming networks which is simpler than previously proposed mechanisms. It allows peers rehabilitation and also permits interaction with potential polluters while they are acting fairly. In case polluters initiate an attack, peers can quickly identify and isolate them. Our results show that the overhead to block polluters is very small compared to the retransmission imposed by polluted data. During an attack, nodes in the proposed P2P system need a retransmission peak of 50% of the original media, while in previous systems they may need more than 100%. Moreover, the proposed system identifies and blocks pollution almost two times faster than other systems and under polluters collusion, it can handle situation without a significant overhead.