35 million Steam users may be at risk after the successful hacking of the network's database, giving unauthorised access to usernames, game purchase information and encrypted credit card details.
Gabe Newell, one of the founders of the game distribution site, says it is as yet unknown whether or not the information has been used.
"We do not have evidence that encrypted credit card numbers or personally identifying information were taken by the intruders,” Newell says in a statement on the site, "or that the protection on credit card numbers or passwords was cracked.
However, Newell says users should still change their passwords, and keep a close eye on their credit card statements.
"We are still investigating.”
The hackers initially defaced Steam’s online forums, and it was investigation of this action that uncovered the breach.
"We do not know of any compromised Steam accounts, so we are not planning to force a change of Steam account passwords (which are separate from forum passwords).
"However, it wouldn't be a bad idea to change that as well, especially if it is the same as your Steam forum account password. We will reopen the forums as soon as we can.
"I am truly sorry this happened, and I apologize for the inconvenience."