The attacks were directed at the Cyworld website as well as the Nate web portal, both run by SK Telecom, which has links to the state monopoly phone company, Korea Telecom.
The breach was revealed by the Korean Communications Commission, which claimed to have traced the source of the incursion back to computer IP addresses based in China, according to the BBC.
Mark Darvill, director of trusted security firm AEP Networks, said although it is too early to say whether this attack is politically motivated or merely an attempt to steal personal information for financial gain, it is becoming increasingly difficult to differentiate between attacks on military, communications, financial, civilian or critical infrastructure targets.
"Across the world, it is private companies and not the public sector that run the majority of the critical national infrastructure, such as telecoms and energy grids," he said.
All organizations involved in the critical infrastructure of a country need to ensure they are co-ordinated within the country they serve, said Darvill, and also that they deploy the absolute highest level of security available.
"This is not only to protect assets and internal sensitive data, but also to guarantee that national security is in no way compromised by individuals, groups or politically motivated government-backed organizations," he said.
This story was first published by Computer Weekly