According to Reuters the National Security Agency led an effort in parallel to the one that went after Iran’s nuclear programme. It developed a similar set of malware that would activate itself only when it encountered Korean language settings on the computers it infected.
Like Iran, North Korea used centrifuges obtained from the Pakistani scientist, A.Q. Khan, who led his own country’s nuclear weapons effort. The P-2 centrifuges used by Iran were controlled by supervisory control and data acquisition (SCADA) systems from Siemens, with control software running on the Windows operating system.
But North Korea’s government tightly controls access to computers and to the Internet meant that the NSA had fewer ways to introduce malware into the computer systems at the Yongbyon Nuclear Research Center, 90 kilometers north of Pyongyang.
It may already have moved past performing uranium enrichment and on to producing plutonium, which would not require centrifuges.
Either way Stuxnet completely failed to stop the North Koreans in their tracks, unlike the Iranians.