Intelligence agencies of South Korea and the United States have issued a joint security advisory on illicit North Korean cyber activities.

South Korea's National Intelligence Service, the U.S. National Security Agency and the Federal Bureau of Investigation issued the first joint advisory between the allies' intelligence authorities on Friday.

The advisory warned that North Korea and its affiliated hacking groups are engaging in attacks on networks of key institutions through malware attacks using fake domains through virtual private networks.

The hacking groups then destroy and encrypt systems with malicious code and demand a ransom in the form of cryptocurrency to restore the systems.

The advisory said that the intelligence authorities of South Korea and the U.S. presume that North Korea is using the cryptocurrency extorted from cyber attacks to finance its prioritized national tasks and intelligence goals.

The release also listed indicators of compromise, including suspicious internet protocol addresses and file names, to facilitate the detection and obstruction of ransomware attacks from North Korean hackers.