SEOUL, Aug, 4 (Yonhap) -- The operator of two popular Web sites was sued Thursday over the leak of personal information of millions of its users following a massive hacking attack last week.

A man, whose surname is Lee, filed the damage suit against SK Communications Co., the operator of the Nate search engine and Cyworld social networking Web site. SK Communications officials had admitted that private information of 35 million users was believed to have been hacked.

The attack was the worst ever online security bleach in South Korea, widely known as the world's most wired country.

Lee, a lawyer by profession and Nate user, demanded 3 million won (US$2,824) in compensation for the leak of his personal information and mental distress that followed, the Seoul Central District Court records showed.

"SK Communication is responsible for its failure to protect personal information which it gained when users signed up," Lee said in the records. "For prolonged mental pains to come from the leak and worries about secondary harm like spam messages, I demand 3 million won in compensation."

On Monday, a similar damage suit was filed against Nate and Cyworld. The complainant asked the court to deliver a summary judgment to order SK Communications to pay 1 million won of compensation for the security bleach.

The attack, in which personal information like names, passwords, mobile phone numbers and email addresses were leaked, is presumed to have been driven by a malicious code from an Internet Protocol address located in China, the company said last week.

A flurry of similar damage suits are expected to ensue, as several Internet communities have been set up to file class-action suits against SK Communications.