Just after the stroke of midnight Pacific time, Valve finally triggered the online authentication system for its new first-person shooter, Half-Life 2, making the game available to thousands of eager gamers worldwide. The company also issued a brief official statement: "Half-Life 2 is available now for purchase and to play. Those who prepurchased their copy via Steam may access the game by double-clicking on the Half-Life 2 icon in their Steam Games directory."

　　This means that those who've either preloaded Half-Life 2 via the Steam service or managed to purchase a retail copy of the game early can finally have at it. This also means that players unwilling to wait through the night for stores to open can theoretically pay for and start playing a digitally distributed copy of the game tonight. Valve's unique digital distribution and authentication system is a necessary step for "unlocking" the game either way. This unlocking process is not instantaneous--it took us approximately 15 minutes on each of several different test systems.

　　In addition to Half-Life 2, an updated version of the original 1998 game Half-Life: Source is also now available through Steam, for those who preordered either the silver or gold packages. However, Day of Defeat: Source, an updated version of a popular multiplayer mod that's also promised as part of the silver and gold packages, is still being listed as "coming soon."

　　Half-Life 2 is the highly anticipated sequel to 1998's classic first-person shooter. For more information about the game, read GameSpot's full review, or our exclusive story of the game's development, The Final Hours of Half-Life 2. To purchase Half-Life 2 online, visit the official Steam Web site.