Online gaming giant Valve has warned users that hackers who defaced its Steam forums on Sunday night gained access to the company's database.
The database contained information including user names, hashed and salted passwords, game purchases, email addresses, billing addresses and encrypted credit card information.
"We do not have evidence that encrypted credit card numbers or personally identifying information were taken by the intruders, or that the protection on credit card numbers or passwords was cracked. We are still investigating," says Valve head gabe Newell.
"We don’t have evidence of credit card misuse at this time. Nonetheless you should watch your credit card activity and statements closely."
According to Newell, only a few forum accounts have been compromised, but it's taking the precaution of asking all furum users to change their passwords.
"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)," he says.
"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."
Valve has over 30 million registered accounts, making this potentially a very serious breach.
Paul Ducklin of security firm Sophos says it's a matter for concern that many companies are encrypting credit card information - they have to, by law - but not the rest of the information they hold about users.
"In my experience, many companies which are PCI compliant have treated that compliance merely as a box to tick," he says.
"They have taken the whole issue of PCI compliance as a security destination to be reached, rather than an excellent starting map for their security journey. That's a pity, and a wasted opportunity to make things better for everyone."