Valve boss Gabe Newell delivered an update to customers following the November hacking of the Steam website and database
. According to an update on the Steam website, Newell explained that the hackers that breached Steam’s security in November may have obtained an encrypted data file that contains the payment transaction details for customers from 2004-2008. This backup file includes user names, encrypted billing address and encrypted credit card information used in those transactions. The good news is that thus far there doesn't appear to be any misuse of that information.
"We do not have any evidence that the encrypted credit card numbers or billing addresses have been compromised. However as I said in November it's a good idea to watch your credit card activity and statements. And of course keeping Steam Guard on is a good idea as well."
As always in such a case of this, it's a good idea to keep tabs on your accounts and credit info. Valve is continuing to work with local law enforcement and users may be receiving a more formal notice in the future.
Source: Steam website
Original Story: Valve Confirms Steam Security Breach