In technical report titled “Vulnerabilities of P2P Systems and a Critical Look at their Solutions”, authors Marling Engle and Javed I. Khan described security problems of peer-to-peer networks and some solutions. Abstract says:
Peer-to-peer systems have emerged from a drive to realize a computing architecture which cannot be taken down by attacking any single point. Scale and massively distributed nature of its architecture are its characteristics defense. Interestingly, these two features also seem to have introduced new set of menacing vulnerabilities. The vulnerabilities become complex due to architectural goals such as load distribution, search facilitation, and easy of reconfigurability. A P2P network must be expanded to include nodes in a potentially unknown environment (such as the Internet). These untrusted nodes may be faulty, malicious, and act together to commit as much damage to the P2P network as possible. In this survey, we discuss some of the vulnerabilities of these P2P systems, and take a critical look at some of their solutions to better understand these new threats.
You can read report here.