U.S. declares North Korea carried out massive WannaCry cyberattack.

The U.S. government is publicly acknowledging that North Korea was behind the WannaCry computer worm that affected more than 230,000 computers in over 150 countries earlier this year.

Trump's homeland security adviser, Tom Bossert, made the announcement in a Wall Street Journal op-ed Monday evening and will follow up with a statement Tuesday morning.

North Korea was widely suspected to have created the virus, which was paired with ransomware that encrypted data on victims' computers and demanded money to restore access. Until now, the U.S. government has not publicly stated as much.

The WannaCry attack, the official said, "demonstrates the importance of basic cyber hygiene, including keeping systems patched and up to date, as well as the need for strong cooperation between public and private sectors to share information, prevent and mitigate cyberthreats."