Files with names in this specific format (Game.Name.vX.X.X.rar) are frequently found on third-party file-sharing sites rather than official storefronts like Steam or GOG . If you did not download this from an official source:
Significant optimizations for turn times and reduced memory usage . Old.World.v1.0.63420.rar
Tribes are now at Peace with each other by default instead of having a Truce. Files with names in this specific format (Game
Run a scan using VirusTotal before opening. Old.World.v1.0.63420.rar
Do you have a (like 7-Zip or WinRAR) installed?