After almost a week of silence, Valve has issued an apology for the leak of private user information on Steam that took place just prior to Christmas, along with an explanation of what went wrong. The problem, which affected approximately 34,000 users, was the result of a caching error that arose out of a denial of service attack against Steam.
“Early Christmas morning (Pacific Standard Time), the Steam Store was the target of a DoS attack which prevented the serving of store pages to users. Attacks against the Steam Store, and Steam in general, are a regular occurrence that Valve handles both directly and with the help of partner companies, and typically do not impact Steam users. During the Christmas attack, traffic to the Steam store increased 2000% over the average traffic during the Steam Sale,” Valve explained in a statement posted on Steam.
“In response to this specific attack, caching rules managed by a Steam web caching partner were deployed in order to both minimize the impact on Steam Store servers and continue to route legitimate user traffic. During the second wave of this attack, a second caching configuration was deployed that incorrectly cached web traffic for authenticated users. This configuration error resulted in some users seeing Steam Store responses which were generated for other users. Incorrect Store responses varied from users seeing the front page of the Store displayed in the wrong language, to seeing the account page of another user.”
The leaked information varied by page request but included users' billing address, the last four digits of Steam Guard phone numbers, purchase history, the last two digits of credit card numbers, and/or email addresses. Full credit card numbers, passwords, or “enough data to allow logging in as or completing a transaction as another user” were not included among the erroneous cache requests, and users who weren't browsing the Steam store during that specific time frame were not affected.
Valve said it is continuing to work with the involved web caching partner to identify users impacted by the leak and improve its processes to ensure this doesn't happen again. “We apologize to everyone whose personal information was exposed by this error, and for interruption of Steam Store service.”