I realize this is not a hacker/cracker forum, but I did find this article interesting:

He also started cracking open North Korea’s official national operating system, called Red Star OS.
Digging into its code he realized that it’s an old and vulnerable Linux version.

https://www.oddee.com/man-takes-down-north-koreas-entire-internet-in-retaliation-to-cyber-attacks-61605/