This book constitutes the refereed proceedings of the 11th International Symposium on Recent Advances in Intrusion Detection, RAID 2008, held in Cambridge, MA, USA, in September 2008. The 20 revised full papers presented together with 16 revised poster papers were carefully reviewed and selected from 80 submissions. The papers are organized in topical sections on rootkit prevention, malware detection and prevention, high performance intrusion and evasion, Web application testing and evasion, alert correlation and worm detection, as well as anomaly detection and network traffic analysis.