Files from unofficial sources carry a high risk of containing malware, miners, or trojans . Since these files bypass official DRM (Digital Rights Management), your antivirus will often flag them. Distinguishing between a "false positive" and an actual threat is difficult.
Because this relates to files downloaded from a third-party repack site rather than an official distributor, Understanding Multi-Part Archives
You cannot open or use part11.rar by itself. You must have every single part (from part 01 to the final part) in the same folder for the extraction to work.