Suspected North Korean hackers managed to break into the Defense Ministry's intranet in August and September past year, but South Korean authorities have previously claimed that nothing significant leaked out.
In a bold move, reports revealed that U.S. President Donald Trump is set to visit the most unsafe border in the world - North Korea's Demilitarized Zone. He revealed that around 235 gigabytes of military documents had been stolen from the Defence Integrated Data Centre, and that 80% of them have yet to be identified.
In response, US President Donald Trump said the US military is "locked and loaded" to deal with North Korea's provocations and North Korea would be met with "fire and fury" if it continued to threaten Washington.
-South Korean plans for a "decapitation" strike against the North Korean regime, a plan that has supposedly angered North Korean dictator Kim Jong Un.
China has taken a series of economic retaliations against South Korea, including a ban on group tours to South Korea, in protest of the deployment of the Terminal High Altitude Area Defense system.
Most recently, North Korea was accused of being behind a cyberattack last year on Bangladesh's central bank that netted $81 million and of masterminding the WannaCry ransomware that rocketed around the world earlier this year.
Commenting on the news is Chris Doman, security researcher at AlienVault, who is investigating hacking groups in North Korea.
The teams held drills in mid-September involving an attack on the South Korea-U.S.
The Defence Ministry had only listed 53GB worth of the stolen data - about 10,700 documents or 22.5% of the total amount.
North Korea has conducted six nuclear tests in recent weeks and launched two missiles over Japan, increasing already fraught tensions between the United States and its allies.
"And finally it is also a message to regional powers that the North is not willing to be pushed around any more and that they intend to continue to develop their economy and their nuclear weapons and missile programs in parallel", he said.