It is, indeed, a frightening scenario—and it isn’t the only threat to the nation’s electricity grid. U.S. critical infrastructure is also vulnerable to cyber and physical attacks. The risk of such attacks is real, and, in some cases, growing. But don’t run out and stock your bomb shelter with whale oil just yet. In fact, odds are you have far more to fear from nut-obsessed squirrels than nutty extremists when it comes to the reliability of your electricity.