The Trump administration on Monday blamed North Korea for launching the “WannaCry” ransomware attack in May, which threatened to destroy data from hundreds of thousands of users unless they paid a ransom through bitcoin.

In an op-ed for the Wall Street Journal, senior White House official Tom Bossert wrote that North Korea was “directly responsible” for the attack, saying his claim was “based on evidence,” though he did not elaborate on what the evidence actually was.

The Washington Post reported earlier Monday that a formal statement from the White House would be released on Tuesday.

The Trump administration has become increasingly hawkish on Pyongyang in what appears to be a creep towards a military stand-off. National Security Adviser H.R. McMaster told a forum in early December that the hermit kingdom was “the greatest immediate threat to the United States” and that the the chances of war were “increasing every day.”

Here’s how bad WannaCry was: