Authorities say they have traced the attack to multiple IP addresses in Shenyang, China.
The group of hackers has leaked documents on five separate occasions over the last week.
The most recent was on Tuesday, which included crucial information about nuclear technology.
Experts say such a leak could be detrimental.
“The hackers says they have about 100-thousand pieces of data. Even if that data is not highly classified, it can be reassembled, creating a huge chunk of new information. Then it becomes very dangerous.”
In response to the recent security breach, the energy ministry conducted a two day-long cyber security drill this week on all of Korea’s nuclear facilities.
The network security of power plants was reviewed as was protocol for shutting them down in the case of a malfunction.
The energy ministry raised its alert level against cyber attacks one notch to the third-highest level on a scale of five on Tuesday.
Connie Kim, Arirang News.