Hackers have gained unauthorised access to Square Enix servers holding details relating to free members in North America and Japan.
It is unknown what data, if any, was compromised, and the server has been taken down for a few days whilst an investigation is carried out and further safeguards implemented.
Square Enix has said there is “no possibility” of any credit card information leak.
“We have reason to believe that unknown parties may have gained unauthorized access to a particular Square Enix server related to the free Square Enix members service offered in North America and Japan,” read a statement from the company.
“In response, Square Enix, Inc. has temporarily suspended operation of the Square Enix members service starting at 10pm (PST) on December 12th, 2011.”
It added: “We are assessing the full extent of this potential breach to determine what data, if any, was compromised and will provide more details as soon as possible.
"While some personal information may have been accessed, we can confirm that there is no possibility of any credit card information leak from this incident, since the server in question stores no credit card information.”
The hack comes after a string of security breaches against games related companies this year, such as Sega, Valve and most famously Sony's PlayStation Network.