Abstract. Recent studies estimate that peer-to-peer (p2p) traffic comprises 40-70% of today's Internet traffic [1]. Surprisingly, the impact of p2p traffic on anomaly detection has not been investigated. In this paper, we collect and use a labeled dataset containing diverse network anomalies (portscans, TCP floods, UDP floods, at varying rates) and p2p traffic (encrypted and unencrypted with BitTorrent, Vuze, Flashget,