Quote from : Space Chronicles: Facing the Ultimate Frontier Book

We conquer the Independence Day aliens by having a Macintosh laptop computer upload a software virus to the mothership (which happens to be one-fifth the mass of the Moon), thus disarming its protective force field. I don’t know about you, but back in 1996 I had trouble just uploading files to other computers within my own department, especially when the operating systems were different. There is only one solution: the entire defense system for the alien mothership must have been powered by the same release of Apple Computer’s system software as the laptop computer that delivered the virus.