Based on the query, you are referring to the classic tactical first-person shooter video game "Project I.G.I.: I'm Going In" (released in 2000), specifically the release by the warez group DEViANCE.
Open Levels: Powered by a modified flight-simulator engine, the maps are vast, allowing multiple routes to infiltrate enemy bases. Critical Reception PROJECT.IGI-DEViANCE
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Tactical Stealth and The "DEViANCE" Era: A Look Back at Project I.G.I. Based on the query, you are referring to