"The government can confirm a cyber attack by unidentified hackers that shut down several sites including the Blue House," the ministry said in a statement, adding that the five-stage national cyber alert had been raised from level one to two.
A number of news media websites and several government agencies, including the office for Government Policy Coordination were also affected by what seemed to be a coordinated attack beginning at 10:45 am.
The ministry statement did not speculate on who might be responsible. Investigations into several recent large-scale cyber assaults on South Korean media groups and financial institutions concluded that they originated in North Korea.
Anonymous denied any involvement on its official Twitter account, but said it had succeeded in hacking a number of North Korean media websites today, including the official Korean Central News Agency (KCNA) and the ruling party newspaper, Rodong Sinmun.