Jul 28, 2011 16:55 GMT  ·  By

South Korea is potentially dealing with its most serious cyber attack in history after the details of 35 million people were stolen from two of the country's largest websites by hackers.

Reuters reports that South Korean authorities are investigating two large data breaches on the Nate portal and Cyworld blogging sites operated by SK Comms.

The Korea Communications Commission said that hackers from China stole names, e-mail addresses, phone numbers and hashed passwords of up to 35 million users.

It's not clear what kind of hashing algorithm was used for the passwords and whether it could withstand brute forcing attempts.

If it's a weak one, the massive compromise would be even more serious because it could extend to people's more sensitive accounts for which many probably used the same password.

South Korean police are investigating the case, but have not yet requested the assistance of Chinese authorities. South Korea is in the habit of accusing their northern neighbours for cyber attacks against its systems.

Back in May, the country's prosecutors accused North Korea of being responsible for an attack against a large local bank that resulted in a three-day outage of its network.

Korean officials have been working on a national cyber security plan to protect the country's critical IT infrastructure after the number of attacks increased in recent years.

In April, hackers managed to breach a server belonging to Hyundai Capital, the country's biggest lender, and stole personal information of around 420,000 consumers. The account numbers and passwords of thousands of prime loan users were also stolen.

China is commonly put forward as a source for cyber attacks, but that doesn't necessarily mean the attackers were located in the country. Hackers are in the habit of routing their attacks through compromised systems in China because they know authorities and companies there don't cooperate with foreign law enforcement agencies.