From this article at the Wall Street Journal:
The Pentagon has concluded that computer sabotage coming from another country can constitute an act of war, a finding that for the first time opens the door for the U.S. to respond using traditional military force… Pentagon officials believe the most-sophisticated computer attacks require the resources of a government. For instance, the weapons used in a major technological assault, such as taking down a power grid, would likely have been developed with state support, Pentagon officials say.
As Lauren Weinstein pointed out on the IP list, you couldn’t possibly come up with a better challenge to incite black hats. “You think only a foreign government can take out a power grid? Well, watch _this_!”