Hackers likely stole encrypted credit card data and data in an attack on gaming company Valve last November.
Attackers were originally thought to have only defaced the company's website forum but Techworld revealed hackers accessed its user database that contained details of some 35 million people including user names, billing addresses, details of game purchases and email addresses.
Valve managing director Gabe Newell said in a message to the forum community there was no evidence that encrypted credit card numbers or personally identifying information was taken.
“We are still investigating,” he said. “I am truly sorry this happened, and I apologise for the inconvenience,” Newell said.
But in an email to Steam users, Newell said it was "probable" that attackers "obtained a copy of a backup file with information about Steam transactions between 2004 and 2008”.
He said the possibility that sensitive transaction data was decrypted should not be excluded.
“The good news is that the credit card details were properly protected as required by PCI, but that's probably not good enough for rebuilding the reputation of the Steam service," SafeNet UK sales director Aydin Ucbasaran said.
He said cryptographic digital keys should be stored in an isolated hardware-based repository.
“This will not only remove the likelihood of hackers stealing the digital keys, but will also ensure the organisation maintains full control of encrypted data even if it falls into the hands of cyber criminals.”