This book constitutes the refereed proceedings of the 11th IFIP TC 6/TC 11 International Conference on Communications and Multimedia Security, CMS 2006, held in Linz, Austria, in May/June 2010. The 23 revised full papers presented were carefully reviewed and selected from 55 submissions. The papers are organized in topical sections on WiFi and RF security; XML and web services security; watermarking and multimedia security; analysis and detection of malicious code and risk management; VoIP security; biometrics; applied cryptography; and secure communications.