North Korean hackers have breached a South Korean military network and have reportedly stolen military “war plans,” a South Korean newspaper reports.

The hack occurred last September, and had originally been downplayed by South Korean defense officials, saying that no critical information had leaked.

Now an anonymous South Korean government source is telling Chosun Ilbo that an official war plan, dubbed OPLAN 5027, was stolen during that hack. The plan is said to contain the joint Republic of Korea-U.S. military plans should a war break out on the Korean peninsula.

The same source has said that “discussions are still taking place” between Republic of Korea (ROK) and U.S. military commanders with regard to changing the plan now that North Korea has access to the documents, either in its entirety or only certain parts.

OPLAN 5027 is a general name for military plans that have existed since 1970s. Throughout its history, it has generally been predicated on initiating following a major ground invasion from North Korea, and had undergone revisions only on a handful of occasions prior to the 1990s. Since the 90s, the plan has been updated every two years to account for changing geopolitical conditions and technological advances.

This is also not the first time that OPLAN 5027 has been hacked. North Korean hackers gained access to what was reportedly an 11-page “executive summary” of the plan in 2009. That hack was blamed on a South Korean military officer who had negligently used a USB flash drive to download the plan.

Despite reports of North Korean military inadequacy (although quantity has a quality all its own), their hackers have been prolific and successful over the last decade. They have stolen U.S. F-15 fighter blueprints, participated in a Bangladeshi bank heist, and perhaps most infamously hacked Sony Pictures in 2014 following their production of “The Interview,” a comedy movie critical of the North Korean dictator Kim Jong-Un.

North Korea is once again at the forefront of U.S. foreign policy concern, with Secretary of Defense James Mattis saying the U.S. will be working with the international community to “get North Korea under control.” President Trump will reportedly pressure Chinese President Xi Jinping to exert more control over North Korea in a meeting between the two leaders this week in Florida.