  Industrial Control Systems (ICS) encompassing resources for process
automation are subjected to a wide variety of security threats. The threat
landscape is arising due to increased adoption of Commercial-of-the-shelf
(COTS) products as well as the convergence of Internet and legacy systems.
Prevalent security approaches for protection of critical infrastructure are
scattered among various subsystems and modules of ICS networks. This demands a
new state-of-the-art cybernetic model of ICS networks, which can help in threat
analysis by providing a comprehensive view of the relationships and
interactions between the subsystems. Towards this direction, the principles of
the Viable System Model (VSM) are applied to introduce a conceptual recursive
model of secure ICS networks that can drive cyber security decisions.
