The White House on Tuesday publicly attributed the 2017 WannaCry cyberattack to North Korea, noting that several U.S. allies stand by the same conclusion after carefully examining the evidence.
"We do not make this allegation lightly and we do so with evidence and we do so with partners," White House homeland security adviser Tom Bossert told reporters.
The May attack cost the U.S. billions, as major industries such as hospitals and financial firms were left with inoperable computers.
"[WannaCry] encrypted and rendered useless hundreds of thousands of computers. It was cowardly, costly, and careless," Bossert wrote in a Wall Street Journal op-ed on Monday.
The administration's conclusion is based on substantial evidence produced by U.S. and British intelligence officials, Bossert said, adding that Canada, New Zealand and Japan all agree that Pyongyang was responsible.
"We took a lot of time to look through classified and sensitive information," he told reporters, when asked if the U.S. was slow to blame North Korea. "We can't get it wrong. We can't rush it."
Despite publicly blaming North Korea for the first time, Bossert said the White House is limited in how it can punish the hermit nation. The Trump administration has already leveled severe economic sanctions against Kim Jong Un's regime over North Korea's continued pursuit of nuclear weapons.