Personal details relating to nearly 1.3 million customers was stolen as part of last week's Sega hack.
1,290,775 Sega Pass members' names, email addresses, dates of birth and encrypted passwords were obtained.
In a statement Sega apologised for the hack, again stressed it does not hold credit card information, and said it had strengthened its network security.
"We express our sincerest apologies to our customers for the inconvenience and concern caused by this matter," Sega said.
"Sega Pass is the service used to provide information about our new products to registered members and does not hold any customer financial information.
"After the unauthorized entry was identified, we immediately stopped the Sega Pass service and took emergency action to prevent further damage. This action included immediately contacting all our registered Sega Pass users. We are now fully investigating the cause of the incident.
"We have also examined the possibility of any other information loss from unauthorized access across our other services and can confirm there are no other verified incidents.
"We will immediately report through the website of Sega Europe Ltd. should there be any further developments regarding this issue.
"We deeply regret that such unauthorized access occurred. We will go on to further strengthen our network security as a priority issue and strive to prevent any potential recurrence."
Sony, Bethesda, Nintendo and Eve Online hackers LulzSec has denied responsibility for the hack – and even offered to help Sega track down the perpetrators.
The Sega hack is the latest in a string of attacks on video game companies this year, seemingly sparked by Sony's suit against PlayStation 3 jailbreaker George "Geohot" Hotz.
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