The Trump administration says computer malware tied to the North Korean government has been targeting US infrastructure and aerospace, financial and media companies for at least nine years to steal information and remotely manipulate networks.
The US has accused North Korea of launching a slew of malicious cyber activity in recent years.
But this warning comes just as the Trump administration is trying to start denuclearization talks with Pyongyang.
The latest warning about malware, called Joanap and Brambul, was issued today as North Korea leader Kim Jong Un dispatched one of his top advisers to New York.
The adviser, Kim Yong Chol, is thought to have been behind a 2014 hack of Sony Pictures Entertainment over a satirical film about a plot to assassinate the North Korean leader.