A representation of the virtual cryptocurrency bitcoin. Reuters-Yonhap

Intelligence agencies of South Korea and the United States on Friday issued a joint security advisory against illicit North Korean cyber activities aimed at stealing cryptocurrencies through ransomware attacks.

The joint advisory by the South Korean National Intelligence Service (NIS), and the U.S. National Security Agency and the Federal Bureau of Investigation warned that North Korea and its affiliated hacking groups are known to engage in shutdowns of networks of key institutions through malware attacks using fake domains through virtual private networks.

According to the agencies, the hacking groups then destroy and encrypt systems with malicious codes in order to extort cryptocurrencies as part of conditions to return the systems back to normal.

The NIS also shared indicators of compromise, such as suspicious internet protocol addresses and file names, to look out for, and shared means of system backups and inspections to prevent cyber attacks and reduce damage.

The advisory was the first of its kind issued by intelligence branches of the South Korean and U.S. governments. The NIS said it will closely cooperate with relevant countries and organizations to prevent damage and respond preemptively to North Korean cyber threats. (Yonhap)