This book constitutes revised selected papers from the 6th International Workshop on Critical Information Infrastructure Security, CRITIS 2011, held in Lucerne, Switzerland, in September 2011. The 16 full papers and 6 short papers presented in this volume were carefully reviewed and selected from 38 submissions. They deal with all areas of critical infrastructure protection research.

Ten National Cyber Security Strategies: A Comparison.- Analysis of Dependencies in Critical Infrastructures.- Assurance and Trust Indicators to Evaluate Accuracy of On-line Risk in Critical Infrastructures.- An Innovative Approach to Emergency Management in Large Infrastructures.- Dynamic Evacuation Guidance as Safety Critical Application in Building Automation.- Defeating Node Based Attacks on SCADA Systems Using Probabilistic Packet Observation.- Sub-optimal Topological Protection Strategy from Advanced Malware.- The Insider Threat in Cloud Computing.- Interdependencies between Critical Infrastructures: Analyzing the Risk of Cascading Effects.- How to Perform Verification and Validation of Critical Infrastructure Modeling Tools.- Petri Net Modelling of Physical Vulnerability.- Investigating the Effect of Network Parameters on Coordinated Cyber Attacks Against a Simulated Power Plant.- The Role of the DNS in the Secure and Resilient Operation of CIs, the Energy System Example.- The Development of Warning, Advice and Reporting Points (WARPs) in UK National Infrastructure.- The Contribution of NEISAS to EP3R.- Policies to Improve Resilience against Major Industrial Accidents.- Fuzzy Input-Output Inoperability Model.- Dependencies Discovery and Analysis in Distributed Systems.- Protecting Critical Infrastructures from Stealth Attacks: A Closed-Loop Approach Involving Detection and Remediation.- Risk Assessment in Critical Infrastructure Security Modelling Based on Dependency Analysis.- Countermeasures Selection via Evidence Theory.- The Robustness of Assortativity.