Even the most powerful cybersoldiers in the world can't hack a country that doesn't have the Internet. The United States learned that the hard way five years ago when the National Security Agency tried and failed to launch a computer virus against North Korea with the ultimate aim of infecting the isolated nation's nuclear weapons technology.

The NSA has long been credited with launching the Stuxnet virus against Iranian nuclear centrifuges in 2009 and 2010. By successfully exploiting a flaw in the Microsoft Windows operating system Stuxnet became what's believed to be the first computer worm that resulted in real-world damages (it destroyed 1,000 or so centrifuges and set Iranian nuclear production back by a number of years). A Reuters report revealed for the first time Friday Iran wasn't the only target, and the NSA deployed a Stuxnet variant against North Korea without achieving the same success.

That's because, unlike Iran, North Korea's population of 25 million is almost completely offline. The so-called hermit kingdom has earned its nickname, with only 1,024 official Internet protocol addresses though the New York Times reported “the actual number may be a little higher.” Such a limited number means the NSA had far fewer ways to introduce malicious software onto computer systems at North Korea's Yongbyon Nuclear Research Center.

North Korea and Iran, which share military technology, are known to have obtained its nuclear centrifuges -- pieces of equipment that enrich particles by spinning them at an accelerated speed -- from A.Q. Khan, a Pakistani scientist who developed his own country's weapons. The centrifuges were operated with data systems from Siemens, which relied on Windows. By tweaking the code used in Stuxnet, an intelligence source told Reuters, the NSA easily could have deployed malware that was activated when translated into the Korean language.

The Reuters report came almost six months after the FBI blamed North Korea for the hack on Sony, which canceled the theatrical release of “The Interview” and prompted international concern over corporate cybersecurity.

While Internet security experts have questioned whether Pyongyang was in fact responsible, the U.S. is almost certainly behind a retaliatory attack that knocked North Korea's Internet offline in December. Unlike a Stuxnet-like malware attack, though, it was a distributed denial of service hack, which involves flooding a system with an overwhelming level of Web traffic, that knocked Pyongyang offline.