Proprietary Alienware

Sobering, on the other hand, is the realization that it is not possible to write viruses on an Apple laptop that are compatible with alien spaceships (as in Roland Emmerich's “Independence Day”).

Oh, I credit Jeff Goldblum as “David” with enough competence to actually pull off programming some kind of virus.
Although the little word virus is happily bandied about by every journalist anyway whenever one piece of software exploits a security hole
in another piece of software.
Much like WinBlaster, which could crash Windows machines, one could assume that David in ID4 merely exploits a security hole in the aliens' network protocol - which, as a radio and TV technician, he studied in depth while everyone around him was panicking - to cripple the aliens' computers and thus their shields as well.

That Emmerich shows this with a haha-gotcha skull in the film is bullshit, of course. In “reality” the Alien-OS equivalent of a blue screen would pop up.

What's far more interesting about this story is not so much the alleged incompatibility of David's code with the aliens' but rather the fact that a 40-year-old alien spaceship has a _current_ security hole in its computer's operating system.
Frightening. That means

1. that the aliens think nothing of open source, where a bug like that would not have survived 40 years in the mothership OS source code but would surely have been discovered in passing by some young alien student, and so Jeff Goldblum, together with Will Smith, would have looked pretty foolish in that parked alien spaceship.
2. that the aliens presumably prefer proprietary software (of course, ossified militaristic hierarchical autocracies go for nothing else) over open source, drag 40-year-old source code along with them, and that “security through obscurity” is the prevailing motto among alien programmers.
3. if we take the alien race that is out to get humanity as a parallel to our civilization in, say, 2,000 years, this means that the development time of operating system successors may behave the same as it does today with Windows Vista. Namely sluggishly.
4. that proprietary software that isn't maintained inevitably leads to the extinction of entire civilizations.

Btw. the program David uses to cripple the aliens' computers is called JollyRoger.c.