The U.S. government has discovered that multiple North Koreans infiltrated leading U.S. mortgage loan companies, according to the head of Washington’s housing finance agency, highlighting the growing threat posed by Pyongyang’s remote workers.

“We recently criminally referred some North Koreans and Chinese for working inside Fannie Mae and Freddie Mac,” Federal Housing Finance Agency (FHFA) Director Bill Pulte said in an interview with Bloomberg TV on Tuesday, referring to the two biggest U.S. government-owned mortgage finance enterprises.

The housing finance chief added that his organization asked the Justice Department to investigate “five or six” North Korean and Chinese nationals posing