Anonymous rejects its involvement in attacks.
The South Korea government websites have been hit with cyber attacks, which have prompted cyber security officials to issue an alert.
Hackers attacked the website of the presidential office among several other official and media sites including North Korea’s Korean Central News Agency, newspaper Rodong Sinmun, and portal Naenara, according to reports.
South Korea Science Ministry said in a statement: "The government can confirm a cyber attack by unidentified hackers that shut down several sites including the Blue House."
The Government Policy Co-ordination office website and some other media servers have also been reported to be affected by the attack.
The unnamed hackers have secured and released openly personal details of over two million South Korean ruling party members and 40,000 US troops, including those positioned in South Korea.
South Korean online security firm NSHC official said: "We have seen the sites where the details were posted and clips that supposedly capture the process of hacking into web sites."
Earlier, South Korea claimed North Korea was responsible for cyber attacks in March 2012 that affected several computers and were also responsible for taking electronic banking sites and ATM networks offline.