They are known to have a 'hackers university', state sponsored thats considered one of the best places to work. Not only are you taken care of and live in a life of luxury, so is your family, and its a pretty good life by all accounts, especially for a NK citizen.
'Hacking' isn't difficult when you're paid to sit around and do it all day long. Any serious network admin knows just how painfully easy it is to get into pretty much any network outside of a place like Google which has the knowledge and understands the dangers of bad IT.
Someplace like Sony? Please, Nessus probably explodes when doing a basic scan of their systems, let alone any actual effort into cracking them wide open.