The US was attempting without success to interfere with the nuclear programme of Pyongyang, in the same way it has done with Iran SCADA systems controlling centrifuges. The NSA failed to spread Stuxnet into North Koreas nuclear plants because they were totally isolated from the rest of the world. North Korea has some of the most isolated communications networks in the world. Just owning a computer requires police permission, and the open Internet is unknown except to a tiny elite. The country has one main conduit for Internet connections to the outside world, through China.”]
Source: http://securityaffairs.co/wordpress/37333/intelligence/stuxnet-against-north-korea.html