Works for Argo, Arma 2:OA, Arma 3 and DayZ

This is a big database containing
every GUID generated from SteamID
76561197960265729 to 76561198450000000
489.734.272 SteamIDs
48,3 GB

284293 GUID's looked up
16071 Unknown GUID's looked up

How to get GUID:
Type #beclient players in game chat