Aliens VS Zombies

Good old Stephen Hawking says that based on the knowledge that there are billions of galaxies which hold  hundreds of millions of stars with planets, the probabilities of aliens walking around those places is plausible. Also he said that those aliens may be organisms living under ice, or evolved resource-hungry travellers who have ruined already their own planets. We have to look at ourselves. To see how intelligent life might develop into something we wouldn't want to meet.