The FBI declared on December 9 that there is “no attribution to North Korea at this point” of the massive cyber attack on Sony Pictures for its planned release of a parody film of North Korean leader Kim Jong-un. Sources close to the ongoing investigations disclosed that Pyongyang remains the principal suspect. Cyber experts concluded that there are similarities between the attack on Sony and earlier attacks against South Korean targets and that malware used included Korean language text.

Earlier this year, Pyongyang had vowed “merciless counter-measures” against the U.S. if Washington failed to block the release of The Interview, a farcical film about a CIA plot to kill Kim Jong-un. The regime characterized the film as an “act of war” and called on both U.N. Secretary General Ban Ki-moon and President Barack Obama to prevent its release. Pyongyang responds forcefully to any perceived insults to its leaders, threatening attacks on South Korean media in 2012 for comparing Kim Jong-un to Adolf Hitler and the South Korean government in 2013 for failing to stop anti–North Korean protests.

Contrary to perceptions of North Korea as a technically backward nation, General Curtis Scaparrotti, the commander of United States Forces Korea, told Congress earlier this year that North Korea has “an active cyber warfare capability.” South Korea’s intelligence agencies warned that North Korea has the capability to “paralyze the U.S. Pacific Command and cause extensive damage to defense networks inside the United States.” A South Korean cyber expert assessed that North Korea’s electronic warfare capabilities were surpassed only by the United States and Russia.

North Korea declared in 2009 that it was “fully ready for any form of high-tech war.” According to South Korea’s National Intelligence Service, North Korean leader Kim Jong-un declared cyber warfare was “a magic weapon” that empowered Pyongyang to launch “ruthless strikes” against South Korea.

The Reconnaissance General Bureau, North Korea’s intelligence agency, oversees Unit 121 with 3,000 “cyber-warriors” dedicated to attacking Pyongyang’s enemies. Seoul concluded that North Korea was behind cyber attacks using viruses or distributed denial-of-service tactics against South Korean government agencies, businesses, banks, and media organizations in 2009, 2011, 2012, and 2013. North Korea also jammed GPS signals in 2012, posing a risk to hundreds of airplanes transiting Seoul’s Incheon airport.

Lieutenant General Bae Deag-sig, head of South Korea’s Defense Security Commander, stated that “North Korea is attempting to use hackers to infiltrate our military’s information system to steal military secrets and to incapacitate the defense information system.” Representative Steve Chabot, a member of the Asia Subcommittee of the House Foreign Affairs Committee, warned that “North Korea’s growing cyber capabilities present the greatest likelihood of a cyber conflict in Asia…. North Korea is not only a nuclear threat, but a serious cyber threat as well.”

Sony has announced The Interview will not be shown in either South Korea or Japan. The studio declined to state the reason but stated the decisions were made prior to the cyber attack.