ANYONE who follows technology or military affairs has heard the predictions for more than a decade. Cyberwar is coming. Although the long-announced, long-awaited computer-based conflict has yet to occur, the forecast grows more ominous with every telling: an onslaught is brought by a warring nation, backed by its brains and computing resources; banks and other businesses in the enemy states are destroyed; governments grind to a halt; telephones disconnect; the microchip-controlled Tickle Me Elmos will be transformed into unstoppable killing machines.

No, that last item is not part of the scenario, mostly because those microprocessor-controlled toys aren’t connected to the Internet through the industrial remote-control technologies known as Scada systems, for Supervisory Control and Data Acquisition. The technology allows remote monitoring and control of operations like manufacturing production lines and civil works projects like dams. So security experts envision terrorists at a keyboard remotely shutting down factory floors or opening a dam’s floodgates to devastate cities downstream.

But how bad would a cyberwar really be — especially when compared with the blood-and-guts genuine article? And is there really a chance it would happen at all?

Whatever the answer, governments are readying themselves for the Big One.

China, security experts believe, has long probed United States networks. According to a 2007 Defense Department annual report to Congress, China’s military has invested heavily in electronic countermeasures and defenses against attack, and concepts like “computer network attack, computer network defense and computer network exploitation.”