"Mirim University produces most of the hackers that get placed in Bureau 121. It's a highly competitive program, with each class accepting only about 100 students out of 5,000 applicants. They take six 90-minute classes every day, learning different coding languages and operating systems, from C to Linux. Jang says a lot of time was spent dissecting Microsoft programs, like the Windows operating system, and how to attack the overall computer IT systems of enemy countries like the US or South Korea."
https://www.businessinsider.com/north-korean-defector-jang-s...
"Mirim University produces most of the hackers that get placed in Bureau 121. It's a highly competitive program, with each class accepting only about 100 students out of 5,000 applicants. They take six 90-minute classes every day, learning different coding languages and operating systems, from C to Linux. Jang says a lot of time was spent dissecting Microsoft programs, like the Windows operating system, and how to attack the overall computer IT systems of enemy countries like the US or South Korea."
Also
https://www.nbcnews.com/news/north-korea/how-north-korea-rec...
https://www.express.co.uk/news/world/913712/North-Korea-late...