South Korea blamed North Korea for hacking an online shopping site in the South and stealing personal records of more than 10 million customers.
The South's national police agency said on Thursday that it had traced the data breach to North Korea's spy agency. The agency said it also detected the same IP addresses and codes which are similar to the ones it had used in previous cyber attacks.
The Online shopping operator Interpark Corp said the hacking took place in May. It said a hacker had sent emails demanding money in bitcoin virtual currency after the cyber attack.
The police said the hacker used common expressions which are mainly used in the North.
The company said it had been cooperating with the police and the money was not paid to the hacker.
"We are sorry that it has become difficult to arrest a suspect as it has been found to be North Korea's conduct," the company said in a statement.
Since the news of the hacking broke on Monday, Interpark's shares have fallen 6 per cent.
This is the latest case of cyber attack by the isolated state and South Korea has been trying very hard to stop such attacks which have become a rising threat in the country.
Recently in June, the police said the North hacked into more than 140,000 computers at 160 Korean companies and government agencies. South Korea has been on high alerts against cyber attacks by North Korea ever since it conducted its fourth nuclear test in January.
South Korea says the North has an effective cyber army which has launched a series of such attacks in the past three years.
However, North Korea has denied all such accusations.