While Trump has threatened to annihilate North Korea, saying the country's leader, Kim Jong Un, "is on a suicide mission", Kim Jong Un has fired back vowing to "tame the mentally deranged US dotard with fire".
The information, that included wartime contingency plans drawn up by the US and South Korea, was from the country's defence ministry, according to Rhee Cheol-hee, a South Korean lawmaker.
"Known as Oplan 5015 - short for 'Operational Plan" - it includes plans for a "decapitation" attack on the Pyongyang leadership, in other words the killing of Kim and his inner circle.
However, the extent of the breach is still unknown, as around 80 per cent of the contents of the 235 gigabytes of leaked data is yet to be identified, Mr Rhee said.
The UK has secretly started drawing up plans for war with North Korea, the Daily Mail has revealed. The US president cryptically added that "only one thing will work" when it comes to dealing with Kim Jong Un's regime, reports the CNN website.
When the hacking attack was found out past year, the Defense Ministry blamed North Korea.
The White House sent an advanced team to Seoul in late September to make preparations.
Pyongyang has repeatedly denied any responsibility for or knowledge of the attacks.
Commenting on the news is Chris Doman, security researcher at AlienVault, who is investigating hacking groups in North Korea. Almost two million South Koreans visited the spot over a decade, according to South Korean government figures.
The US president is expected to send a "significant message" to Kim Jong-un either verbally or "kinetically" as part of his first visit to South Korea amid tensions on peninsula in November.
Trump has not shied away from making strong statements on North Korea in the past but has not gone through with any military steps that depart from orthodoxy.
The two nations have been at verbal loggerheads over the North's nuclear activities, with the United States pressing for a halt to missile tests and Pyongyang vowing to continue them.