The Steam forums were hacked in Nov 2011. The hackers got access to a DB with Steam users' personal information.
http://arstechnica.com/gaming/2011/11/valve-confirms-steam-h...
http://arstechnica.com/gaming/2011/11/valve-confirms-steam-h...
No company is immune from hacking, the best anyone can hope for is secure hashing functions are in place and that financial and user account data are properly separated.