Counter-Strike (commonly abbreviated to CS) is a tactical first-person shooter video game which originated from a Half-Life modification by Minh \"Gooseman\" Le and Jess \"Cliffe\" Cliffe, and features real-world weapons. The game has been expanded into a series since its original release, which currently includes Counter-Strike: Condition Zero, Counter-Strike: Source, Counter-Strike: Anthology and Counter-Strike on Xbox. Counter-Strike pits a team of counter-terrorists against a team of terrorists in a series of rounds. Each round is won by either completing the mission objective or eliminating the opposing force. The latest incarnation of the game, Counter-Strike: Source, is based on the Source engine developed for Half-Life 2. The game has both individual and multiplayer options. Bots can be added into the game. The online-multiplayer option is activated via Steam. Other than similarities in basic gameplay, Counter-Strike is not in any way related to Half-Life. The original version was marketed as a commercial mod, but since then it has grown into a separate game in itself. The most recent versions do not require Half-Life to play, unlike a mod, and are no longer marketed as Half-Life: Counter Strike. Counter-Strike is the most widely played online first-person shooter in the world.[verification needed] In 2002 there were over 30,000 populated Counter-Strike servers on the Internet (second place was Unreal Tournament with about 9,800). In 2004, GameSpy statistics showed over 85,000 players simultaneously playing Counter-Strike at any point in time, and in 2006, Steam regularly shows over 200,000 players for Counter-Strike[1] (this includes Counter-Strike: Source, Counter-Strike: Condition Zero and Counter-Strike). According to statistics gathered by Valve\'s content-delivery platform, Steam, these players collectively contribute to over 6.17789 billion minutes of playing time each month, as of February 5, 2007,[1] solidifying its position as the most popular online first-person shooter of all time