The private data of more than 13 million MapleStory players was compromised in a recent hacking incident.
According to a report in the Korean Herald, the attack took place last Thursday, and reached around three-quarters of the game's player-base - 13.2 million people.
The compromised data included player names, user IDs, passwords, and registration numbers - the Korean equivalent of a US social security or UK national insurance number.
A spokesman for Nexon, the Korean publisher that operates MapleStory, confirmed that overseas players were not affected.
"We operate separate servers in each country. Only Korean users' information was affected," he said.
The attack is the second largest of its kind in the country's history. It is currently under investigation by the Korea Communications Commission.
Nexon was planning an IPO valued at $1.3 billion in the next few weeks. At the time of writing, the company had not announced any amendments to its plans as a result of the attack.