The White House publicly blamed North Korea for May's massive WannaCry attacks, which locked more than 300,000 computers across 150 countries, Homeland Security adviser Tom Bossert said at a Tuesday morning briefing, according to NPR.
"North Korea has acted especially badly, largely unchecked, for more than a decade," Mr. Bossert said, adding that the WannaCry attacks were reckless and caused "havoc and destruction."
WannaCry was a ransomware attack that exploited a vulnerability in older versions of Microsoft's Windows operating system. Security experts traced the exploited weakness back to the U.S. National Security Agency and determined it was part of stolen NSA cyberweapons known as EternalBlue.
In June, the NSA linked North Korea to the attacks in an internal assessment that was not made public. The U.K., whose National Health System endured the brunt of its effects, also said it was "as sure as possible" North Korea was to blame.
"We believe now we have the evidence to support this assertion," Mr. Bossert said, according to NPR. "It's very difficult to do when you're looking for individual hackers. In this case, we found a concerted effort."
Mr. Bossert called the attacks, which demanded a ransom from its victims, "cowardly, costly and careless," adding that officials are still unsure how much money the attacks raised.
"The consequences and repercussions of WannaCry were beyond economic," he wrote in an opinion piece published in The Wall Street Journal Monday. "The malicious software hit computers in the U.K.'s healthcare sector particularly hard, compromising systems that perform critical work. These disruptions put lives at risk."
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