The incident at Nintendo is extremely minor compared with the hacker attacks on rival Sony Corp.'s PlayStation Network and other online services since April that have led to a personal data breach involving more than 100 million user accounts. The Nintendo breach involved no sensitive information and hasn't caused any damage to its operations or inconveniences for its customers, the company said.
Still, the incident at another global gaming giant raises a question over whether any online services can be fully protected from potential hacking attempts.
A hacker group called Lulzsec, which had earlier claimed that it had broken into some of Sony's websites and stolen customer data, posted on the Internet some data it claims is a "server configuration file," or data for programming purposes, from a Nintendo server.
Nintendo spokesman Ken Toyoda acknowledged that there has been an unauthorized access to the company's U.S. server, but stressed that the accessed information didn't include any information on the company, or any personal data for its customers.
"We are always working to make sure our systems are secure," he said.
After Lulzsec posted the data online, the group said on its Twitter account that it was not targeting Nintendo. "We sincerely hope Nintendo plugs the gap," it said.
The attack comes as Nintendo this week launches its new online service for its 3DS hand-held game machine.
The Nintendo e-Shop, where 3DS users can buy and download games, including some classic titles remade in 3-D, will be available in the U.S. from Monday and in Japan from Tuesday.
The 3DS, which went on sale in February in Japan and in March in the U.S., allows users to play 3-D games without requiring them to wear specialized glasses.