The hacking attacks on Tuesday, the anniversary of the start of the Korean War in 1950, brought down the main websites of South Korea's presidential office and some local newspapers, prompting cyber security officials to raise the alert.
The identity and motives of the attackers were not immediately clear, but the reports come as cyber security and surveillance have become a global issue, with the United States seeking fugitive former security contractor Edward Snowden who leaked details about US surveillance to the media.