cyber defense computersREUTERS/Jim UrquhartA monitor displays an attacking team's progress during a drill at a Department of Homeland Security cyber security defense lab at the Idaho National Laboratory in Idaho Falls, Idaho, September 30, 2011.


North Korea's isolation from the world, coupled with its abundance of heavy weapons pointed towards South Korea's capital and largest airport, limits a lot of the US's options in responding to Pyongyang's alleged involvement in the Sony hack.
But there are other, less conventional options available to the US, Joseph Marks reports for Politico. 
North Korea is already a pariah, so further sanctions or the listing of Pyongyang as a state sponsor of terrorism would have little effect. Instead, cyber attacks that threaten to undermine the state's edifice of control may be the most effective route for the White House's promised "proportional response." 
Bruce McConnell, a former Department of Homeland Security cyber counsel, told Politico that one option would be for US government hackers to wage cyber psychological warfare. This could include the dispersal of articles from The New York Times and other publications that belittle Kim Jong-Un and the North Korean regime.
Internet access is extremely limited in North Korea and it's possible that only elites or people already closely allied with the regime would see the results of these efforts. But even this could raise the specter of internal revolt and deter the Kim regime from further provocative action.
Another possible response would be for the US government to buy "The Interview" from Sony and then distribute the video freely online, Martin Libicki, a senior management scientist at RAND, told Politico. The free distribution of "The Interview" could lead to the film's eventual propagation throughout North Korea, possibly humiliating the Kim regime and threatening its control over the country. 
Human rights groups have already proposed delivering copies of "The Interview" into North Korea by balloon. The New York-based Human Rights Foundation (HRF), in conjunction with South Korean group Fighters for a Free North Korea, have already started raising donations to put such a plan into action. 
HRF in the past has floated political leaflets, USB drives, and DVDs of media like Desperate Housewives into the Hermit Kingdom from South Korea. 
Beyond measures aimed at loosening support for the North Korean regime, the US could also theoretically engage in retaliatory cyber attacks. These attacks could target pieces of North Korean infrastructure while risking a possible kinetic response against South Korea. 
North Korea's hacking of Sony was an unprecedented cyber attack that leaked terabytes of information across the web. Subsequent threats of terrorist attacks aimed at theaters led to Sony completely pulling "The Interview" from theaters.