Blue's News has linkage to Wired and BBC stories expanding on the story of the source code stolen from Valve by crackers, as well as word from Valve's own Gabe Newell, via Shacknews, on how the attackers gained entry. Apparently they used a remote administration tool as well as a few other things to gain access to their internal network over the Internet. They are still finding machines that have been compromised, and are also unsure about how the crackers gained access initially.