.rar files from third-party sites are common vectors for malware. Always run a scan before extracting.
Searching for "RimWorld.v1.4.3549.rar" typically points toward archived versions of the game found on file-sharing or pirate sites. If you are looking for a "good piece" regarding this specific version, here is the context on why it matters and what you should know. What is Version 1.4.3549? RimWorld.v1.4.3549.rar
Users typically look for specific version archives for two reasons: RimWorld.v1.4.3549.rar