Stephen Hawking is wrong. Any aliens that are technologically far in advance of us, so that they are capable of intergalactic travel, would have to be benevolent. If they weren't benevolent, they would have destroyed themselves long before. It is obvious that our own species is fast approaching the point at which we either learn to live together in peace with each other and our planet, or we will wreck the planet and kill ourselves in the process. We will be tested in many ways: over food, water, energy supplies, and so on. If we act in a way which benefits the whole human race, we will flourish. If we greedily try to defend our privileges, we will all die together. Any aliens that travel across the galaxy will have to pass those tests first.

I think that Stephen Hawking has been watching
DVDs of the film Independence Day too often. Great entertainment, but the premise of malevolent aliens is rubbish.