The personal information of 35-million South Koreans were compromised by a massive hacking that is being blamed on the Chinese.

SK Communications Co., which operates South Korea's third most popular Internet portal, unearthed the hacking on Tuesday.

Koo Ki-hyang, a spokeswoman at the company, told the Yonhap news agency that SK’s Nate search engine and Cyworld social networking web site were hacked by malicious code.

That code was apparently traced to an Internet Protocol address based in Mainland China, Koo said. However, SK was unable to identify when the information was hacked or who was behind the cyber attack.

Information accessed included passwords, mobile phone numbers, and email addresses, according to the company. South Korean police said they will launch a formal probe into the hacking affair.

The incident might be the biggest breach of online security in South Korea since a cyber-attack on a unit of eBay impacted 18-million users three years ago.

"Police will first determine whether the hacking was conducted internally or by an outsider," said an official at the country’s Cyber Terror Response Center, a police division dealing with cybercrimes.

"We will also look into whether the customer information leak was triggered by malicious Internet Protocol codes from China.”

The attack on the popular websites come on the heels of the hacking of several government ministries and financial companies in South Korea, which resulted in the theft of personal data of millions of people.