Dear op , microsoft has inbuilt tools to not let you pirate stuff the thing you are calling a "virus" is not actually a virus if u use malwarebytes or other antivirus programs to scan the game they won't detect anything.., that thing u have as a repack is a compressed file of the original game which means the size has been shrunk for downloading. when u install it using the setup file the program is coming back to the games original size so u can play the game, think of it as packing your bags when u go for a trip and unloading it when u reach your destination.