Last week, a massive private data breach struck Nexon’s extremely popular massively multiplayer online game, MapleStory that affected nearly three quarters of the 18 million players. According to the MMO publisher, much of the sensitive stolen information had been encrypted; however, as a matter of course, the company is suggesting that users change their passwords anyway.

After discovering on Thursday that the breach had happened, Nexon was quick to placate global users fears that their data might have been struck. The Korea Herald brings us details on this story,

“We operate separate servers in each country,” said a Nexon spokesman. “Only Korean users’ information was affected.”

Of the data stolen, millions of users suffered the breach of their IDs, player names, passwords, and residential registration numbers.

Resident registration numbers are more or less an equivalent to social security numbers in the United States. These numbers are used by the government of Korea to enforce curfews on underage gamers in MMOs by restricting the times that they can play, according to an April 2010 article in the Korea Herald. Underage gamers are asked by the Ministry of Culture to opt for a six-hour blackout period during every day and given three options: midnight-6 a.m., 1-7 a.m., and 2-8 a.m.

The hack has been reported by Nexon to the Korea Communications Commission, the ruling body regulating telecommunications, on Friday and requested a police investigation.

According to the Herald, this comes weeks before a planned IPO by the company’s Japanese affiliate. The MMO publisher is rumored to be seeking $1.3 billion in its initial public offering in Tokyo on Dec. 6.

This marks yet-another-breach of an online game for Korea, with the last being the attack on Korean social game Cyworld blamed on Chinese hackers. That breach led to the leak of the records of 35 million players.

As more and more users go to the Internet for entertainment and seek massively online games, breaches such as happened to Sony’s PlayStation Network, Nexon’s MapleStory, and SK Communications Cyworld will continue to mount in numbers. While media attention for these events runs in spikes, the attacks themselves occur in tides and trends none of which ever recede much.

In this instance, Nexon had encrypted their sensitive information and users should seek to protect themselves by changing passwords across games—and should be security conscious and use different passwords for different games.