In the movie, a race of aliens that travel to Earth, a planet that consists of more than 2/3's water, is weak to water. 

Logic. 

Also how or why such an advanced race needed to create "signs" in the form of crop circles instead of using some kind of like high-tech mapping from their ships is another story, or why they didn't just bomb the fking planet from orbit is beyond anything I've ever seen before.

@Draco

And using that fact, then it's equally as possible for "Anti-EMP" to exist. Also, what makes it so certain that an Alien technology uses circuits and transistors that would be effected by EMP?