In Independence Day, why are the destroyers the size of a city when the actual weapon takes up a few blocks at most? If they made the destroyers smaller they could build more and attack more cities at once. However, having a large surface just above the city being destroyed channels the energy from the central weapon, making the weapon many times more efficient. — Anemone
Also, their entire civilization is contained solely in the mothership and those destroyers. A destroyer isn't a military vehicle; it's an entire military base and the surrounding town to boot. They don't just fly the things; that's their home. It makes sense that it would be built for all the size they can afford to give it, as this is where they spend their entire lives.
The idea of uploading a virus to the alien mothership is the subject of much ridicule. However there's actually an explanation that makes this slightly plausible, at least in terms of movie logic. When the crashed alien ship is first shown it is stated that the wreak was the source of all the modern advances of the last 50 years. Our computer technology could potentially be compatible with that of the aliens because it's based on that of the aliens.
Lack of security in their computer network is also somewhat understandable — they communicate telepathically, and are "like locusts". Very probably they have some version of a Hive Mind, which would preclude the need for that much security, as no-one would sabotage themselves. They just didn't consider that one of their victims would find a way in and use it against them.
