The United States accused North Korea on Monday of being behind the WannaCry cyber attack that affected hundreds of thousands of computers in 150 countries this past May.

In a Wall Street Journal op-ed, President Donald Trump’s homeland security and counterterrorism advisor Thomas Bossert said that “after careful investigation” the U.S. “publicly attributes the massive ‘WannaCry’ cyber attack to North Korea.”

The U.S., Bossert said, was making the allegation “based on evidence,” though he did not cite any specific proof for the government’s claim. Instead, he noted that “other governments and private companies” have drawn the same conclusion regarding