On behalf of the Program Committee, it is our pleasure to present the p- ceedings of the 12th International Symposium on Recent Advances in Intrusion Detection systems (RAID 2009), which took place in Saint-Malo, France, during September 23-25. As in the past, the symposium brought together leading - searchers and practitioners from academia, government, and industry to discuss intrusion detection research and practice. There were six main sessions prese- ingfullresearchpapersonanomalyandspeci?cation-basedapproaches, malware detection and prevention, network and host intrusion detection and...