Electric utilities are concerned about "hacker attacks" on their computer systems. Computers guide America's electrical grids -- they monitor and control circuits.

Inducing an electrical blackout on a national scale is an offensive "three-fer": 1) an attack on key infrastructure; 2) an economic assault (damaging commerce); and 3) a psychological attack seeding hysteria and perhaps producing political panic.

Other scenarios worry defense planners. Commercial air service can be hampered or halted by attacking air traffic control system computers. Trucking can be crippled by attacking the computers controlling fuel supplies (refineries, pipelines, storage sites and distribution systems).

Space satellites and their computer-controlled ground stations offer another target. An attacker who interferes with ground-to-satellite communications could conceivably disrupt Global Positioning System (GPS) navigation, deny satellite weather data, "blind" spy satellites, and cut some phone and television networks.

Uncertainty of the "origin of the attack" makes cyber attacks attractive. In cyberspace, the difference between a criminal act and an act of war is often a matter of interpretation as well as degree.

But U.S. defense officials are becoming increasingly vocal about "probes" and "intrusions" traceable to nation-states. Last month, The Wall Street Journal quoted a "senior intelligence official" as saying: "The Chinese have attempted to map our infrastructure, such as the electrical grid. So have the Russians." The article noted that cyber "intruders" had not (as yet) attempted to damage the grid but "could try during a crisis or war."

Cyberspace is complex. While specific computers and control systems are vulnerable to attack, several cyber warriors make the case that knocking out the entire Internet and simultaneously disrupting "hardened" U.S. military communications is a difficult if not impossible task. "Anti-intrusion" and "anti-virus" defenses for computers are also improving.

Chilton's statement, however, serves as diplomatic notice that "classical deterrence" -- assured counter-attack with the full range of U.S. military and police power -- is now an element of American "cyber defense."