Internet became today a medium of sharing large amount of data among different nodes situated anywhere in the world. Due to its fairly open nature Peer to Peer applications gain-ing popularity in sharing of large data rather then conventional client-server systems. Many P2P applications has been designed for the purpose of content distribution over Internet and most of them are based on decentralized Peer to peer architecture. Although absence of a central server, peers can communicate directly but lacks of central administration makes P2P network vulnerable to various kind of attacks. Authenticity of data become a major challenge in decentralized P2P content distribution applications since peers are unknown to each other within a network. To ensure the data authenticity, several schemes had been proposed by trust and reputation systems in recent past few years. In literature, we have covered the desirable characteristics of trust and reputation systems. Trust and reputation system play a vital role in defining the trustworthiness of a peer before making transaction. On the basis of trust value requester can able to skip malicious identities. However due to malicious behaviour of peers, they themselves are vulnerable to various kinds of attacks. The paper reviews existing collusion attacks.

1. Fabiola Bento Soares, Newarney Torrezao da Costa, Luis Fernando. Faina, and Jamil Salem Barbar. A reputation system model based on indication to combat pollution in p2p networks. In CTRQ 2012, The Fifth International Conference on Communication Theory, Reliability, and Quality of Service, pages 45–50, 2012.
2. Jau-Shien Chang and Hao-Jhen Wong. Selecting appropriate sellers in online auctions through a multi-attribute reputation calculation method. Electronic Commerce Research and Applications, 10(2):144–154, 2011.
3. Cristiano Costa and Jussara Almeida. Reputation systems for fighting pollution in peer-to-peer file sharing systems. In Peer-to-Peer Computing, 2007. P2P 2007. Seventh IEEE International Conference on, pages 53–60, IEEE-2007
4. Ernesto Damiani, De Capitani di Vimercati, Stefano Paraboschi, Pierangela Samarati, and Fabio Violante. A reputation-based approach for choosing reliable resources in peer-to-peer networks. In Proceedings of the 9th ACM conference on Computer and communications security, pages 207–216. ACM, 2002.
5. Kevin Hoffman, David Zage, and Cristina Nita-Rotaru. A survey of attacks on reputation systems. 2007.
6. Sepandar D Kamvar, Mario T Schlosser, and Hector Garcia-Molina. The eigentrust algorithm for reputation management in p2p networks. In Proceedings of the 12th international conference on World Wide Web, pages 640–651. ACM, 2003.
7. Eleni Koutrouli and Aphrodite Tsalgatidou. Taxonomy of attacks and defense mechanisms in {P2P} reputation systemslessons for reputation system designers. Computer Science Review, 6(23):47 – 70, 2012.
8. Eleni Koutrouli and Aphrodite Tsalgatidou. Taxonomy of attacks and defense mechanisms in p2p reputation systemslessons for reputation system designers. Computer Science Review, 6(2):47–70, 2012.
9. Stephanos Androutsellis-Theotokis and Diomidis Spinellis. A survey of peer-to-peer content distribution technologies. ACM Computing Surveys (CSUR), 36(4):335–371, 2004.
10. Qiao Lian, Zheng Zhang, Mao Yang, Ben Y Zhao, Yafei Dai, and Xiaoming Li. An empirical study of collusion behavior in the maze p2p file-sharing system. In Distributed Computing Systems, 2007. ICDCS'07. 27th International Conference on, pages 56–56. IEEE, 2007.
11. Petros Maniatis, TJ Giuli, Mema Roussopoulos, David SH Rosenthal, and Mary Baker. Impeding attrition attacks in p2p systems. In Proceedings of the 11th workshop on ACM SIGOPS European workshop, page 12. ACM, 2004.
12. Felix Gomez Marmol and Gregorio Mart´?nez P´erez. Security threats scenarios in trust and reputation models for distributed systems. Com-puters & Security, 28(7):545–556, 2009.
13. Sergio Marti and Hector Garcia-Molina. Taxonomy of trust: Categoriz-ing p2p reputation systems. Computer Networks, 50(4):472–484, 2006.
14. John Risson and Tim Moors. Survey of research towards robust peer-to-peer networks: search methods. Computer networks, 50(17):3485–3521, 2006
15. Li Xiong and Ling Liu. Building trust in decentralized peer-to-peer electronic communities. In Fifth International Conference on Electronic Commerce Research (ICECR-5). Citeseer, 2002.
16. Li Xiong and Ling Liu. A reputation-based trust model for peer-to- peer e-commerce communities. In E-Commerce, 2003. CEC 2003. IEEE International Conference on, pages 275–284. IEEE, 2003.

P2p Trust Reputation Collusion Attacks Identity Attacks