protecting or attacking stalker camps or searching for treasure. The AI characters travel around the entire Zone as they see fit. Several attack tactics were cut for difficulty reasons, including the ability for enemies to heal wounded allies and give orders. S.T.A.L.K.E.R. uses a heavily modified version of the ODE physics engine. Ragdoll physics, destructible objects, realistic bullet ballistics and skeletal animation can all be found in the game. Bullets are affected by gravity, bounced against solid surfaces at oblique angles, and firearms are highly inaccurate when fired without aiming. To score consistent hits at medium or long range, players must aim using the iron sights on their guns. Additionally, hit damage is pseudo-realistic, and the player can die after only being shot a few times (although later in the game various armor suits and artifacts can be acquired that increase the player's resistance to damage). Late-game depends heavily on scoped weaponry due to the well-armed and armored enemies that keep their distance from the player. A weather system is integrated into various parts of the landscape and allows a variety of weather effects, such as sunshine, storms and showers. The weapons available, behavior of the AI, game tactics and ranking systems depend on the weather. Unlike most dynamic weather systems, the game features complete dynamic wet surfaces such as pavement, concrete, brick walls, etc. The game features ambient music by Vladimir Frey aka "MoozE". It also has three songs from the Ukrainian band Firelake. Development and release The game was first announced by GSC Game World in November 2001, as S.T.A.L.K.E.R.: Oblivion Lost, although it had been talked about as early as 2000. It had its release date, originally as summer 2003, pushed back several times. Meanwhile, hundreds of screenshots of the game had been released, as well as a dozen preview video clips, accompanied by other forms of promotion by GSC, such as inviting fans to their offices in Kyiv to play the current build of the game. However, due to the delays some considered S.T.A.L.K.E.R. to be vaporware. In late December 2003, a pre-alpha build of the game was leaked to peer-to-peer file sharing networks. This build, marked as version 1096, inadvertently acted as a fully functional tech demo of S.T.A.L.K.E.R.'s engine, despite its lack of NPC enemies and fauna. After that, with the game missing the 2003 release date and still far from being finished, the