
Visible crew/equipment: When Dr. Okun is about to unlock "the vault", and says, "The freak show," a crewmember wearing a black and white striped shirt is hiding under the vault's floor, right behind Okun. (Only visible on fullscreen DVD.)

Directed by: Roland Emmerich
Starring: Will Smith, Bill Pullman, Jeff Goldblum, Randy Quaid, Vivica A. Fox, Harry Connick Jr., Mary McDonnell, Brent Spiner, Judd Hirsch
They disable the destroyers by uploading a computer virus into the mother ship, which is blown up with a nuke.
The Green Flame Torch

Visible crew/equipment: When Dr. Okun is about to unlock "the vault", and says, "The freak show," a crewmember wearing a black and white striped shirt is hiding under the vault's floor, right behind Okun. (Only visible on fullscreen DVD.)
President Thomas Whitmore: I don't understand, where does all this come from? How do you get funding for something like this?
Julius Levinson: You don't actually think they spend $20,000 on a hammer, $30,000 on a toilet seat do you?
Trivia: In Area 51 there is a large screen displaying the results of the nuclear strikes against the alien ships. Look under the screen and there is some text in green. Pause it to read the following: "The purpose of these green lines is to lead you to believe that these words mean something", and "And can I see with eye serene the very pulse of the machine Wordsworth".
Question: It's been shown in the film the the aliens are technologically more advanced than us. Then, how come, with all their technology, they were unable to defend themselves from something as simple as a computer virus?
Answer: It was also a bit of a tribute to "War of the Worlds", in which the alien invaders with much more advanced technology ultimately succumbed to ordinary terrestrial pathogens in the original novel by H. G. Wells as well as its many screen adaptations.
Chosen answer: Its supposed to be an exercise in demonstrating how the aliens underestimated their opponent, but in reality it's merely a convenient plot device.
Answer: I was wondering the same thing. Since the Harvesters had our satellites meant they could eavesdrop on every single conversation. David and other people in the facility probably put up a firewall on the computers and cameras, so that the aliens couldn't see or hear what they were planning on doing.
Answer: Maybe there were no viruses in the planet where these aliens came from so they didn't have any countermeasures against them.
Answer: They could defend against it, hence why they bring the nuke. The virus drops the shields, and the nuke destroys The Mother Ship. David even says that the shields will be down for a few minutes.
Answer: Remember that the aliens had to interface with our satellite computer code first...David simply "reverse engineered" the code to create the virus. When it was uploaded, they didn't have enough time to combat it.