A North Korean hacking group that extorted virtual currency worth around one-point-five billion U.S. dollars last month has converted at least one-fifth of the seized amount into cash.

According to BBC on Sunday, the Lazarus Group is believed to have turned into cash at least 300 million dollars worth of digital tokens stolen from crypto exchange ByBit on February 21.

While ByBit has managed to track down and freeze 40 million dollars worth, it failed to prevent some from being converted into cash.

Experts affiliated with crypto investigators Elliptic say that 20 percent of the funds have now "gone dark," and are unlikely to ever be recovered.

Dr. Tom Robinson, co-founder of Elliptic, said North Korea is the best at laundering crypto and that the hacking team is known to be working nearly 24 hours a day to transfer the virtual currency into cash.

The United States and allies suspect that Pyongyang has carried out a number of hacking attacks in recent years to finance the regime's military and nuclear development.