—The recent surge of peer-to-peer (P2P) networks consisting of thousands of of hosts makes them a breeding ground for malware proliferation. Although some existing studies have shown that malware proliferation can pose significant threats to P2P networks, defending against such an attack is largely an open problem. This paper aims to develop the countermeasure that can effectively mitigate the malware proliferation while preserving P2P networks’ performance. To this end, we propose a dynamic trust management scheme based upon localized trust evaluation and alert propagation which prevents innocent peers from downloading files from infected peers. Our analysis and experimental results show that our approach can effectively reduce the malware proliferation rate.