The U.S. could suffer a nationwide blackout if just nine of the country's 55,000 electric-transmission substations were knocked out on a particularly hot day, the WSJ reports, citing a study from the Federal Energy Regulatory Commission.
The U.S. could suffer darkness "for weeks, if not months," the WSJ writes.
Utilities aren't required to protect vital substations unless they're located at nuclear facilities, although regulators are considering increasing security standards.
Meanwhile, nearly all utilities that took part in a drill last year to assess their ability to cope with online and physical attacks admitted they weren't prepared enough, a report from the North American Electric Reliability Corp shows. Over 2,000 participants from the U.S., Canada and Mexico were involved in the exercise.