In a press statement issued late on Friday, Sega said that its Sega Pass online system had been shut down, and an investigation was under way.
The MSNBC newswire quoted Yoko Nagasawa, a Sega spokeswoman, as saying that the company is deeply sorry for the trouble caused for its customers and that the firm wanted to strengthen its security.
"The attack against Sega, a division of Sega Sammy Holdings that makes game software such as Sonic the Hedgehog as well as slot machines, follows other recent significant breaches including Citigroup, which said over 360,000 accounts were hit in May, and the International Monetary Fund", noted the newswire.
Sega Europe, a division of Sega that runs the Sega Pass network, immediately notified Sega and the network customers after it found out about the breach on Thursday, Nagasawa told the newswire.
Although initial reports blamed the LulzSec hacktivist group for the Sega attack, the company has offered to track down and punish the hackers who broke into Sega's database.
The BBC newswire, meanwhile, quotes an email sent to Sega Pass users on Friday as saying that "over the last 24 hours we have identified that unauthorized entry was gained to our Sega Pass database."
"We immediately took the appropriate action to protect our consumers' data and isolate the location of the breach. We have launched an investigation into the extent of the breach of our public systems."
According to the BBC, Sega said it has reset all passwords and "urged customers to change their log-on details on other services and websites where they used the same credentials."