As a beta participant, once you've verified your email address with Steam, Steam Guard becomes available for your use and is enabled for your Steam account by default.

With Steam Guard enabled, anyone attempting to login as you from an unrecognized computer must first provide additional, one-time authorization. A special access code will be sent to your contact email address, and this code must be entered into Steam before your first login on an unfamiliar computer is complete. You will also be notified if any login attempts from computers other than those you've authorized occur. Steam Guard essentially acts as a form of "User Rights Management," where you as the user have greater control over access to your stuff.

"Account phishing and hijacking are our top support issues," said Gabe Newell, President of Valve. "With Steam Guard, we've taken a big step towards giving customers the account security they need as they purchase more and more digital goods."

Gabe demonstrated further development of Steam Guard today at the CeBIT computing trade show in Hannover, Germany. In addition to email-based authentication, Steam Guard will soon offer other forms of secondary authentication, such as Intel® Identity Protection Technology, a hardware-based security feature available with the new 2nd Generation Intel® Core™ and Core™ vPro® processors. With IPT, secondary authentication is effortless, as it is provided by the chipset itself.

To opt into the latest Steam client beta and begin protecting your account with Steam Guard, launch the Steam client and visit Steam Settings' Account tab, then changing your beta participation to “Steam Update.”