White House homeland security adviser Tom Bossert said Monday the United States believes North Korea was behind the "WannaCry" cyberattack earlier this year.
He continued, "The attack was widespread and cost billions, and North Korea is directly responsible."
North Korea has rejected accusations that it has been involved in hacking.
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.
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."
Pointing to threats outside of North Korea, Bossert said preventing similarly massive cyber incidents would take concentrated effort and that President Donald Trump had taken steps in the right direction, such as ordering the modernization of government information technology to enhance the security of US computer systems and the sharing of software vulnerabilities with developers.