Hackers have broken into computer systems and data has been lost at the South Korea"s nuclear plant operator, but the nuclear reactors are completely safe.
The nuclear plant operator, Korea Hydro and Nuclear Power Co Ltd (KHNP), blamed "elements who want to cause social unrest" for the hack, but it said there was no risk to nuclear reactors.
It said "It is 100 percent impossible that a hacker can stop nuclear power plants by attacking them because the control monitoring system is totally independent and closed."
An anti-nuclear protester did claim responsibility for the attack on Twitter and demanded aging nuclear reactors be shutdown or they would leak documents, but the message could not be verified.
The attack comes amid the ongoing Sony hack and news that North Korea is building cyber-warfare capabilities in a secret government department called "Bureau 121".
Obsessed by fears that it will be over-run, a defector said "North Korea"s ultimate goal in cyber strategy is to be able to attack national infrastructure of South Korea and the United States."