Abstract
National and international security, our financial, industrial as well as economic prosperity, healthcare system and national well-being as a whole are dependent on critical infrastructures, which could be described as highly interdependent. Many examples are available such as the national electrical grid, oil and natural gas systems, telecommunication and information networks, transportation networks, water systems, and banking and financial systems. Keeping them in reliable and secure state and study their dependencies is paramount for every government or organization. There is an urgent need of their classification. Creation and development of model and methodology which could describe their behaviors is going to make this world safer. The presented here model and based on it study and initial results are steps toward reliable and secure critical information infrastructure.