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© Kim Jae-hwan / Reuters
North Korean hackers reportedly accessed computer systems of the Daewoo shipbuilding company, stealing blueprints of South Korea's newest warships, including Aegis-class destroyers and submarines.

Seoul is "almost 100 percent certain that North Korean hackers were behind the hacking and stole the company's sensitive documents," Kyung Dae-soo, an MP from the Liberty Korea opposition party, told Reuters on Tuesday.

He said the intrusion was detected by a Defense Ministry unit in charge of investigating incidents of cybercrime. It is yet unknown how sensitive and classified the stolen files were as investigators chose not to reveal such details, Kyung added.

The investigation concluded that it was likely North Korean hackers as their methods have been very similar to other attacks that North Korea was thought to be behind, the MP added.

Daewoo Shipbuilding & Maritime Engineering (DSME), founded in 2000, has built several warships for the South Korean Navy, including the Aegis-capable Sejong the Great-class destroyers, Yi Sun Shin-class missile frigates and Son Won Yil-class diesel-electric submarines.

DSME is also known as one of the largest manufacturers of tankers and container ships. In 2012, the company was awarded a $598 million contract to build four 37,000-ton double-hulled tankers for Britain's Royal Fleet Auxiliary.

A spokeswoman for Daewoo Shipbuilding told Reuters she was unaware of the issue until early Tuesday, adding the company is set to confirm Kyung's report. North Korea is believed to have been behind several major cyber incidents in the past few years, although Pyongyang has always either denied or ignored the allegations.

Earlier in October, Rhee Cheol-hee, a ruling party MP and member of parliamentary defense committee, said 235 gigabytes of South Korean military files were stolen from the Defense Integrated Data Center back in September 2016. The documents reportedly include war plans prepared by the US and South Korea, along with details on power plants and military facilities.

Also earlier this year, South Korea's National Intelligence Service accused Pyongyang of attempting to hack into railway control systems and intercept officials' mobile devices. North Korean hackers allegedly penetrated the smartphones of dozens of senior South Korean officials, stealing text and voice messages, Yonhap news agency reported.

The hacking allegations triggered a response in the US as well, with President Donald Trump directing the Cyber Command to target hackers in North Korea's intelligence agency, the Reconnaissance General Bureau. The US Cyber Command attacked its computer servers with traffic that choked off internet access, according to the Washington Post.