May the US government monitor private critical infrastructure assets to combat foreign cyberspace threats?

The government “owns” the entire US airspace–it can install radar systems, enforce no-fly zones and interdict hostile aircraft. Since the critical infrastructure and the associated cyberspace are just as vital to national security, could the US government protect major assets–including privately-owned assets–by positioning sensors and defensive systems? This paper discusses the legal issues related to the government’s deployment of sensors in privately owned assets to gain broad situational awareness of foreign threats. This paper does not necessarily advocate pervasive government monitoring of the critical infrastructure; rather, it attempts to analyze the legal principles that would permit or preclude various forms of monitoring.