This book constitutes the refereed proceedings of the 9th International Symposium on Recent Advances in Intrusion Detection, RAID 2006, held in Hamburg, Germany in September 2006. The 16 revised full papers presented were carefully reviewed and selected from 93 submissions. The papers are organized in topical sections on anomaly detection, attacks, system evaluation and threat assessment, malware collection and analysis, anomaly- and specification-based detection, and network intrusion detection.