The South Korean government has accused North Korea of hacking a nuclear power provider and stealing secret data.
A report claims that North Korean hackings were able to take data from the Korea Hydro and Nuclear Power (KHNP) company, which runs the 23 nuclear reactors in the country.
The attackers were said to have threatened “destruction” via Twitter, demanding the shutdown of at least three reactors, but the report maintains only “non-critical” systems were actually compromised.
North Korea was said to have launched 5,986 phishing attacks to more than 3,500 employees of the company, in order to access internal systems.
Bloomberg reports that blueprints of South Korean plants were leaked on Twitter last week, by an account holder claiming to be based in Hawaii.
South Korea said that IP addresses used by the attackers could be traced to the North, and added that a key virus used in the attack was reminiscent of previous hacks by the secretive regime.
The attacks in question took place in December, around the same time of a separate hacking attack on Sony Pictures which was subsequently blamed on Pyongyang by US officials.
"We condemn North Korea's persistent cyber terror targeting of our country and the international community,” the South Korean Ministry of Unification said in a statement.
North Korea denies involvement in the attacks.
The English language state media said of the ministry on Wednesday: “The puppet forces' operation of such sinister plot-breeding body in broad daylight means clear denial of the ideology and social system of the DPRK and, at the same time, an unpardonable anti-reunification criminal act of reneging on all agreements reached between the north and the south till now.”