This book constitutes the refereed proceedings of the 6th International Conference on Mathematical Methods, Models, and Architectures for Computer Network Security, MMM-ACNS 2012, held in St. Petersburg, Russia in October 2012. The 14 revised full papers and 8 revised short presentations were carefully reviewed and selected from a total of 44 submissions. The papers are organized in topical sections on applied cryptography and security protocols, access control and information protection, security policies, security event and information management, instrusion prevention, detection and response, anti-malware techniques, security modeling and cloud security.