Screens went blank early in the afternoon, with skulls popping up on some screens – a strong indication that hackers had planted a malicious code in South Korean systems, the state-run Korea Information Security Agency said. Some computers started get back online after nearly three hours.
Police and South Korean officials investigating the shutdown said the cause was not immediately clear, but speculation centred on North Korea, with experts saying a cyber attack orchestrated by Pyongyang was probably to blame.
The shutdown came amid rising rhetoric and threats of attack from Pyongyang in response to UN punishment for its December rocket launch and February nuclear test. Washington also expanded sanctions against North Korea this month to try to cripple the regime’s ability to develop its nuclear programme.
North Korea has threatened revenge for the sanctions and for continuing routine US-South Korean military drills it considers invasion preparation.
Accusations of cyber attacks on the Korean Peninsula are not new. Seoul believes Pyongyang was behind at least two cyber attacks in 2011 and 2012.
The latest paralysis took place just days after North Korea accused South Korea and the US of staging a cyber attack that shut down its websites for two days last week. The Thai-based internet service provider confirmed the stoppage, but did not say what caused the shutdown in North Korea.
“It’s got to be a hacking attack,” Lim Jong-in, dean of Korea University’s graduate school of information security, said. “Such simultaneous shutdowns cannot be caused by technical glitches.”
Shinhan Bank reported that the shutdown hit online banking and cash machines. At one coffee shop in central Seoul, customers were asked to pay cash for their coffee and queues formed beside jammed cashpoints. Seoul has become largely cashless as many people use debit and credit cards.
Broadcasters KBS and MBC said their computers went down at 2pm but officials said the shutdown did not affect broadcasts.
The YTN cable news channel said its computer network was paralysed while local TV screened footage of workers staring at blank screens.