Screenshot/edition.cnn.comA nuclear plant in South KoreaSouth Korea's nuclear plant operator has been breached, raising fears that North Korea could have targeted key pieces of infrastructure in its southern neighbor before employing similar attacks against the US.
Currently, South Korean authorities are claiming that only non-critical information about the plants have been leaked, The Guardian reports. The stolen information include personal data for approximately 10,000 employees, at least two reactor designs, and electricity flow charts.
So far, no blame has been placed on North Korea for the attack. However, the malware and code that was used in the nuclear plant hacks resemble code previously used by Pyongyang.
Lim Jong In, a cyber security expert who works with South Korea's military, told CNN that he believes that there could be a link between the attacks. The current round of hacking bears resemblance to both the Sony hack and a previous attack on South Korea's media, banks, and ATMs in 2013.
In a particularly ominous message on a hacking site, Lim told CNN that the group responsible for targeting the nuclear operator said, "if they don't stop the operation of the nuclear power plant, they will destroy it." 
Screenshot/edition.cnn.comLim Jong In
According to Lim, the attack on the nuclear operator could indicate a pattern. First, North Korea carries out an attack on South Korea, before staging a more refined attack abroad against the US.
On Sunday, the hackers threatened further action on Thursday unless three power plants were shut down. Despite the serious nature of the hack, South Korea has sought to reassure its citizens.
"It is 100% impossible that a hacker can stop nuclear power plants by attacking them because the control monitoring system is totally independent and closed," an official at Korea Hydro and Nuclear Power (KHNP) told The Guardian.
KHNP is holding two days of drills against possible cyberattacks following the release of the nuclear plant information.