Aliens of some sort have to exist somewhere, whether they're fully sapient and living among us, or simple life forms made of amino acids and DNA molecules. We exist here on our planet-there's gotta be others somewhere.
I mean, life is a chemical reaction, by their very definition chemical reactions can be recreated with relative ease.
So life DOES exist, though how far away and in what form it shall take is unknown to us, life on other planets would be given a different set of "building blocks" than life on ours, essentially, any lifeform we find could be different in every imaginable way to us.
I think where there is smoke, there is fire. There is just too much public and private information and substantiation to ignore the possibility that intelligent life not only exists but has had contact on Earth. Personally I lean toward belief though it scares the hell out of me.
What a relief, the last person to talk about DNA said it proved god existed. Aliens yes i'd say there is a good probability, I'm assuming they don't wish to wreck us up otherwise it would have happened already.