Hackers gained access to the United States power grid, including detailed drawings that could have been used to cut power to millions of people, according to a new Associated Press report.

The report, published Monday, indicated that there have been roughly 12 times in the past 10 years when foreign hackers accessed the networks controlling lights across the United States.

That includes one instance where hackers, believed to be from Iran, had swiped passwords and detailed sketches of dozens of power plants, invaluable tools if one planned to cut off the power. Cybersecurity experts told the Associated Press the breach (which affected energy company Calpine, which operates 83 power plants) dates to at least August 2013 and could be ongoing.

The Associated Press reported that hackers accessed passwords that could have been used to access Calpine’s networks remotely, along with highly detailed drawings of 71 energy-related facilities across the country. That could allow skilled hackers to specifically target certain plants.

But targeting a plant and successfully shutting off the power are two different things.

The Associated Press report noted the power grid is designed to keep the lights on when utility lines or equipment fail. To cause a widespread blackout, a hacker would have to be exceptionally skilled, bypassing not only a company’s security measures but also creating specialized code that disrupts the interactions of the company’s equipment. Still, experts told the AP that it remains possible for a sufficiently skilled and motivated hacker to send a large swath of the country into blackout, and enough intrusions have occurred that a foreign hacker can likely “strike at will.”

The Associated Press report was published the same day the Wall Street Journal unveiled that Iranian hackers accessed the controls of a dam about 20 miles away from New York City in 2013.

In another breach, tech company Juniper Networks announced last Thursday that it discovered some “unauthorized code” in its software that could have allowed skilled hackers to improperly access some devices and decrypt secure communications. CNN reported the FBI is investigating the hack because it fears the code might have been used to spy on government correspondence.

Because government use of Juniper products is so widespread, one U.S. official told CNN the hack was like “stealing a master key to get into any government building.” CNN reported a foreign government is believed to be behind the hack, but it still is not clear who is responsible.

Juniper said it released a patch that corrects the issue. The company said it wasn’t aware of “any malicious exploitation” of the security loophole, but noted there likely wasn’t a way to reliably detect if a device had been compromised because hackers could have easily erased the evidence.