Tokyo-based online game publisher Nexon has confirmed that millions of Korean user accounts for its MapleStory online game have been compromised as part of a security breach.

However, the company was quick to stress that the breach does not affect user accounts in countries outside of Korea.

The breach was discovered last week, and has affected around three quarters of the 18 million MapleStory users in South Korea.

User IDs, users' real names, passwords and residential registration numbers were leaked by as-of-yet unidentified hackers. The company said that the data was encrypted, but advised users to change their passwords on other websites.

Users outside of Korea need not worry, explained a Nexon spokesperson to the Korea Herald newspaper. "We operate separate servers in each country. Only Korean users' information was affected," it said.

The breach comes just weeks after Nexon revealed that it is heading for an initial public offering on the Tokyo Stock Exchange next month.