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 On Christmas Day, Steam users woke to a bewildering series of problems. Users reported seeing wish lists, game libraries, and personal account information that wasn’t their own. Email addresses, partial credit card numbers, and phone numbers were all shared, with no explanation of why or how. Steam has published an update on what happened, and explained the bizarre behavior.

First, Valve wants to reassure users that while an estimated 34,000 people found themselves with someone else’s account, none of the details that leaked were enough to allow someone to either steal an account or to complete transactions with the available credit card information. The concern here would be that addresses or other forms of personally identifiable information (PII) could be harvested from Steam and then matched against other databases of stolen personal data. Hacking groups have proven adept at finding and exploiting such opportunities.

SteamWinter

Steam Winter Sale + DDoS? Bad idea.

Imagine that you use three different services, all of which are hacked. Hack #1 exposed your username and an encrypted form of password that can be cracked with sufficient effort. Hack #2 leaks your billing address, while Hack #3 leaked credit card information and a name associated with the account. Individually, all three are annoying. Combine them, and an attacker can do serious harm. Given that we’ve seen large corporations wait weeks or months before disclosing the extent of a data breach, it’s possible for your personal data to be compromised long before you’re aware to even look for a problem.

So what went wrong?

Here’s Valve explanation in its own words:
“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.
“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.”
Once Valve realized it was under attack, it shut the Steam Store down and manually configured a new caching configuration, tested it, and purged all of the previous data before bringing Steam back online. The company has promised to reach out to everyone affected by the problem and to continue investigating to ensure no critical information was leaked.