North Korea Behind Massive Cyberattack Earlier This Year, U.S. Government Says

North Korea was behind a massive cyberattack that affected more than 150 countries earlier this year, President Donald Trump’s homeland security adviser revealed in a Wall Street Journal piece Monday.

The invasive “WannaCry” attack affected more than 230,000 computers across the globe for several days in May, shutting down universities, warehouses and banks. It also managed to put hospital systems in the U.K. on lockdown.

“After careful investigation, the U.S. today publicly attributes the massive ‘WannaCry’ cyberattack to North Korea,” Tom Bossert wrote in the WSJ. The rogue state will be held accountable, he said.

“North Korea has acted especially badly, largely unchecked, for more than a decade, and its malicious behavior is growing more egregious. WannaCry was indiscriminately reckless,” he wrote.

Bossert urged governments and businesses to cooperate to mitigate cyber risk and increase the cost to hackers. But, he said, the U.S. is willing to act alone “to impose costs and consequences for cyber malfeasance.”

He also called on the private sector to increase its accountability by “taking actions that deny North Korea and other bad actors the ability to launch reckless and destructive cyberattacks.”

In June, the National Security Agency linked North Korea to the WannaCry worm, the Washington Post reported.

The worm took the form of a ransomware attack, seizing and encrypting computers and demanding payment to release files.

The attack was “unprecedented” in scale, European policing agency Europol said at the time.

In October, the British government also publicly declared it believed North Korea was the culprit.