Anyone Out There?

Data from the Kepler space observatory suggests planets capable of supporting life are far more common than previously thought and our galaxy probably contains at least two billion planets that, like Earth, have liquid water on their surfaces and orbit around their parent stars in the habitable zone for life.
Quite a fascinating thought and hopefully we will be sending probes to these places to look for life out there somewhere although i do worry of the consequences of what we would do, or what they would do to us if we ever made contact.
Human history is full of stories of one group of humans discovering another lot and then killing them and stealing their land and resources so don't expect things to be any different if they have six legs and live in another Solar System.
Then there is the problem of what if they have the same tendencies as us but are more developed and have bigger and better weapons, we could be vapourised before we even get to lie that we come in peace.
I do sometimes wonder that if we did find a hospitable planet with no occupants that we could colonise, we would then expand out across the solar systems and the Universe creating a network of new human civilisations.
Then i think, what if something from another planet discovered Earth and started colonising it a couple of million years ago. We could just be one in a chain of some other planets inhabitants civilisations so instead of humans populating the Universe, we are one of a number of someone else's civilisations. 
Would explain all the UFO's that keep buzzing us, it's the things from the Parent Planet seeing how the colony of funny creatures with the two eyes and two arms they left here millions of years ago are getting on.