SEOUL, March 17 (UPI) -- South Korea's unification ministry said Tuesday North Korean hackers were responsible for infiltrating multiple servers at Korea Hydro and Nuclear Power and for launching six cyber-attacks that attempted to steal sensitive data and the personal information of employees.
The attacks occurred in December following a separate hacking incident involving Sony Pictures which the U.S. government blames on North Korea.
"The hackers threatened to endanger South Koreans and national security," Seoul's unification ministry said in a statement.
The Wall Street Journal reported a string of phishing e-mails tried to bait users to give up passwords so hackers could obtain remote access to their computers. The ruse had mixed results but another hacker posted URL links to Korea Hydro's internal data archives and threatened to leak more data while issuing demands. Nuclear power plants, however, were not compromised.
Yonhap reported North Korea's state-controlled media outlets dismissed Seoul's statements, and denied any North Korean involvement with the hacking of nuclear power data.
North Korean media Uriminzokkiri said the South Korean conclusion was "ignorant, heavy-handed and nonsensical," adding that the close timing of the hacking to the Sony Pictures incident was giving the South Korean government an opportunity to sell the incident as a North Korean act.
The North Korean statement however did not comment on Seoul's other findings, including its discovery of a North Korean IP address that was used to penetrate South Korean servers, and a malignant code used previously by North Korean hackers.
The Wall Street Journal reported other tweets posted by the hackers were posted through servers in Shenyang, China and Vladivostok, Russia.