For 40 years, astronomers have fired microwaves off objects to chart near-Earth space and track the movement of close asteroids - and these signals are traceable back to us. By comparison, Zaitsev says, dedicated transmissions - often described as "shouting into an unknown jungle" - are a mere whisper. He calculates the astronomy signals have filled an area of the sky 2000 times greater than dedicated broadcasts have managed to dateMaybe when they show up they'll merely want to serve man.
Surprisingly enough, communicaiton with extraterrestrial intelligence has recently become a topic of serious debate. (See David Brin's cogent argument against such communication.) It would be foolish to assume that all alien species are nicer and higher-minded than we. While it might not be possible for aliens to colonize Earth, there's a considerably lower barrier to launching self-replicating weapons at us. Before you scoff, think about the debate that we humans would have if we discovered a high-tech civilization nearby, along with evidence that it was at least moderately aggressive.
Something to think about when you've managed to achieve that perfect paranoid mood.