A South Korean lawmaker says that hackers from North Korea have stolen plans jointly developed with the United States for a “decapitation” operation aimed at assassinating Pyongyang’s top leadership.

If true, this represents more than just a serious breach of security — it means that North Korean leader Kim Jong-un can now plan a counter-strategy to foil any attempt by U.S. and South Korean forces to take him out.

Rhee Cheol-hee, a lawmaker with South Korea’s ruling Democratic Party, said hackers penetrated the Defense Integrated Data Center in September 2016 and stole a number of classified documents.

Previous reports in South Korean media noted the breach but downplayed its seriousness. Now, Rhee says the defense ministry still has to identify the content of about 80 percent of the 235 gigabytes of data that was stolen.

“The Ministry of National Defense has yet to find out about the content of 182 gigabytes of the total (stolen) data,” the lawmaker said in a statement quoted in the South Korean news agency Yonhap.

Among the data stolen where Operation Plans 5015 and 3100. Previous reports noted that OPLAN 5015 includes a pre-emptive strike on the North’s nuclear and missile facilities, as well as “decapitation attacks” against Kim and the rest of the North Korean leadership.

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