The legitimate csinativeimagegen.exe from Microsoft is completely safe.
It is typically found in the installation folder of recent CSI products and should be run after a clean install to optimize performance. csinativeimagegen.exe
Microsoft includes a scheduled task called or similar. It runs at system idle time or after updates to recompile native images. This task invokes csinativeimagegen.exe in the background without any user prompt. The legitimate csinativeimagegen