President Trump's national security adviser said Monday that officials aren't sure who is behind a global cyberattack that has hit major companies in more than 100 countries.

"We don't know. That's the attribution that we're after right now," said Tom Bossert, Trump's cybersecurity adviser. "It would be very satisfying for me and for all of our viewers I think if we find them and bring them to justice."

"Attribution can be difficult here," he added. "I don't want to say we have no clues as I stand here today. I feel that the best and brightest are working on that."

Hundreds of thousands of computers were hit by the "ransomware" known as "WannaCry," which disrupts those computers and demands a ransom as the price for returning those computers to their regular state.

Bossert said so far, no U.S. government computers have been hit by the cyberattack.