Aliens that will terrify humanity (science video).

Aliens are often written into Science Fiction novels and films as both as our potential saviours and good chums (would you like a Wookie with that, sir), as well as the stuff of utter nightmares.

So, would an alien civilization from the stars prove benevolent towards us or our end? And how the heck would our polluting, warlike, unreasonable bipedal ape civ look like to them?