Hawkings says aliens exist

Steven Hawking is a true genius. He says aliens exists, but they may be dangerous he warns. That reminds me of a joke about a man. He said he had seen aliens, and they were not green. However, they were taking about a green card - to regularize their own status in america.

First I believe there are many aliens and they are well aware of us. If they had wanted to eliminate us, they could have done this a long time ago.