Industrial Control Systems (ICSs) are of the most important components of National Critical Infrastructure. They can provide control capabilities in complex systems of critical importance such as energy production and distribution, transportation, telecoms etc. Protection of such systems is the cornerstone of essential service provision with resilience and in timely manner. Effective risk management methods form the basis for the protection of an Industrial Control System. However, the nature of ICSs render traditional risk management methods insufficient. The proprietary character and the complex interrelationships of the various systems that form an ICS, the potential impacts outside its boundaries, along with emerging trends such as the exposure to the Internet, necessitate revisiting traditional risk management methods, in a way that treat an ICS as a system-of-systems rather than a single, one-off entity. Towards this direction, in this paper we present enhancements to the traditional risk management methods at the phase of risk assessment, by utilising the cybernetic construct of the Viable System Model (VSM) as a means towards a holistic view of the risks against Critical Infrastructure. For the purposes of our research, utilising VSM's recursive nature, we model the Supervisory Control and Data Acquisition (SCADA) system, a most commonly used ICS, as a VSM and identify the various assets, interactions with the internal and external environment, threats and vulnerabilities.
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