Forty years ago this week, lightning struck an electrical power station, blacking out the city of New York and surrounding suburbs. Believe it or not, such a scenario is even more likely now, thanks to North Korea.

That’s because America’s electrical grid has become increasingly reliant on digital control systems since 1977, making it more vulnerable to an outage. And now, the possibility of a terrorist attack, most likely to be launched by North Korea, means the entire country could be plunged into darkness.

Even worse, due to the high degree of digital reliance, restarting a power plant that has gone offline is more difficult than in times past.

“The grid has become highly automated and, if remote digital communication goes down, you need someone at the substation to flip the switch to turn it back on after an outage,” says Tom Popik, chairman of the Foundation for Resilient Societies, which has been warning for years about the threat to America’s electric supply system.

That point was underscored last weekend, when a heatwave knocked out a power station in the San Fernando valley of Los Angeles. Though terrorism was quickly ruled out, the effect was the same: more than 100,000 residents were left without power.

And that’s the best kind of blackout. The nightmare scenario is an attack on the grid from an electro-magnetic pulse weapon, or EMP. North Korea is believed to have purchased the necessary technology to create an EMP from a Russian supplier more than ten years ago. If that technology has been sufficiently developed, a North Korean EMP could be launched via rocket into space, and detonated. The resulting pulse waves could knock out multiple power stations in the U.S., and cause a domino effect.

Ironically, the U.S. power grid is now more susceptible to such an attack than it was forty years ago, when New York City went dark. “The electric grid is only intended to withstand individual failures,” Popik warns. “The grid is far less resilient now than it was even in the 1940s.”

That’s because electricity supplied by natural gas is no longer backed up by oil tanks. Those tanks were removed because of environmental concerns, and besides, it’s cheaper to burn natural gas than fuel oil. As an example, in California, 97% of generation capacity had backup oil tankers onsite in 1996. Today that figure is 29%.

“I think we are living in an age of misplaced priorities and excess optimism,” Popik says. “I think the optimism is that long-distance delivery of electricity and gas will always be reliable. In an age of cyber-attack and physical attack, the reality could be startlingly different.”

It’s time to flip on the switch in our thinking about our energy security. Power on.