Isn't there a Bond movie about this?
Cyberspies have penetrated the U.S. electrical grid and left behind software programs that could be used to disrupt the system, according to current and former national-security officials. [...] Intelligence officials worry about cyber attackers taking control of electrical facilities, a nuclear power plant or financial networks via the Internet.
If there's a policy implication here, it should be to recast the debate over the smart grid. (A debate that was last seen in the stimulus bill.) Either that, or we should hire a legion of more advanced super spies.
I can't really speak to the merits, but the Center for American Progress has a report (PDF) arguing that an updated grid is a national security priority, in addition to an energy priority.
Update: A well-placed source reminds me that attacks on the US power grid resemble the plot of Live Free or Die Hard more than any Bond movie.