WASHINGTON (Reuters) – U.S. government officials warned on Wednesday about the threat of North Korean hackers, calling particular attention to banking and other finance.

The reason for the advisory – which was jointly issued by the U.S. Departments of State, Treasury, and Homeland Security, and the Federal Bureau of Investigation – was unclear. North Korean hackers have long been accused of targeting financial institutions, and the content of the warning appeared to draw on material already in the public domain.

Requests for comment sent to the U.S. agencies were not immediately returned. The North Korean mission to the United Nations in New York did not immediately respond to a request for comment.

North Korea is alleged to be behind an ambitious, years-long campaign of digital theft, including siphoning tens of millions of dollars in cash from ATMs, carrying out gigantic thefts at major banks, extorting computer users worldwide, and hijacking digital currency exchanges. The global money-grab has been a topic of increasing international concern.

Last year, for example, a U.N. report said that North Korea had generated an estimated $2 billion for its weapons of mass destruction programs using “widespread and increasingly sophisticated” hacking efforts.

In Wednesday’s advisory, U.S. officials said North Korea’s online activities “threaten the United States and countries around the world and, in particular, pose a significant threat to the integrity and stability of the international financial system.”

(Reporting by Lisa Lambert, Tim Ahmann, and Raphael Satter in Washington. Additional reporting by Michelle Nichols in New York. Editing by Steve Orlofsky)