South Korea issued a cyberattack alert yesterday after hackers penetrated several official websites, including the presidential Blue House, on the anniversary of the outbreak of the Korean War.
"The government can confirm a cyberattack by unidentified hackers that shut down several sites including the Blue House," the science ministry said.
It said the five-stage national cyberalert had been raised from level one to two.
News media websites and several government agencies, including the office for Government Policy Coordination and the ruling New Frontier Party, were also affected by what seemed to be a coordinated attack starting at 10.45 am. The Blue House website carried a message saying the site was "under maintenance".
The hacking coincided with the 63rd anniversary of the start of the Korean War on June 25, 1950. The ministry statement did not speculate on who might be responsible.
Investigations into several recent large-scale cyberassaults on South Korean media groups and financial institutions concluded that they originated in North Korea.
Posts left on the hacked sites claimed to be the work of the global "hacktivist" group Anonymous and included messages praising North Korean leader Kim Jong-Un.
Anonymous denied any involvement on Twitter, but said it had succeeded in hacking several North Korean media websites on Tuesday, including the official Korean Central News Agency and the ruling party newspaper, Rodong Sinmun. Both sites were briefly inaccessible yesterday morning but appeared to be running normally a few hours later.
South Korea has sought to beef up its cyberdefences since a March 20 attack completely shut down the networks of three television broadcasters and crippled operations at three banks.
An official investigation determined North Korea's military intelligence agency was responsible, with a joint team of civilian and government experts tracing the origin to six personal computers used in North Korea.
About 48,700 machines including PCs, automatic teller machines and server computers were damaged in the attack, which coincided with heightened military tensions on the Korean peninsula. North Korea was also blamed for cyberattacks in 2009 and 2011 that targeted South Korean financial and government agencies.
In testimony last year to the US congressional Armed Services Committee, the commander of US forces in South Korea, General James Thurman, said North Korea was employing "sophisticated computer hackers" trained in cyberattacks.
"Such attacks are ideal for North Korea" because they can be done anonymously, and "have been increasingly employed against a variety of targets including military, governmental, educational and commercial institutions", Thurman said.