They say strangers are just friends you haven't met yet - but it's not a view Stephen Hawking shares. In a new documentary series for the Discovery channel, he suggests that we should be avoiding making contact with aliens at all costs.

Life, he suggests, is likely to be widespread in the universe, though the odds are that most of it will take the form of microbes or simple animals. But if there is more developed life, we should be careful.

"One piece of advice that Professor Hawking doesn't mind sharing is the less-popular notion that it might be better if we kept our location a secret rather than being so anxious to make contact," says Discovery.

"Reaching out to the stars with our messages of curiosity and peace may only make it easier for an advanced alien mining operation to stake a claim on Earth. First contact would be a much better proposition if we can wait until we are on more equal terms."

Hawking compares making contact with alien species with Native Americans' first contact with Christopher Columbus - which didn't turn out brilliantly for the Native Americans.

"I imagine they might exist in massive ships... having used up all the resources from the planet below," Professor Hawking says.

"Such advanced aliens would perhaps become nomads looking to conquer and colonise whatever planets they could reach. If so, it makes sense for them to exploit each new planet for materials to build more spaceships so they could move on."

Professor Hawking suggests that one massive source of energy available to advanced alien civilizations would be the ability to tap and concentrate the radiant energy of stars with an array of planet-size collectors.

You can see a clip of some of the alien conceptions from  Into the Universe with Stephen Hawking, here.