How vulnerable is our nation's power grid to an electromagnetic bomb?

Cell phones, computers, transportation and water systems, all connected to the nearly 500,000 miles of transmission lines traversing the U.S. If a foreign enemy injects an electromagnetic pulse or emp into the U.S. power-grid, either by bomb or hacking, the results would be cataclysmic.

"Is it a problem? You bet it's a problem. I'm afraid that it's a kill-shot," said Frank Gaffney, Center for Security Policy.

There are three major sectors of the U.S. power grid; the eastern, western and Texas interconnections. The Department of Energy says roughly 125 million U.S. households rely on this network daily.

If a bomb or a hacker infects these grids with an EMP it can release a seismic burst of energy frying all circuits within a massive radius of ground zero.

Without power, it could leave millions of Americans without transportation, water, refrigeration and food.

Homeland Security says response plans like stockpiling emergency generators are already in place but experts say in many cases, that's futile. Because knocking out the grid could likely be the first of a two-pronged attack.

"In other words, I shut out the power-grid, I shut out the lights in the city, then I have a secondary attack like a bombing, so I create chaos on top of chaos," said Dr. Tyrone Powers.

Terror groups like ISIS don't have the technical know-how for EMP's but Dr. Powers says nations like Iran likely do, "We've said to them over an over again, 'should you mount that kind of attack on the U.S. we will consider that an act of war.'"