As in Extra Terrestrial?
My personal, uninformed, opinion: Do aliens exist now, previously or in some time to come? Earth as a single planet has life. But a single item of data is impossible to extrapolate to give any meaningful statistics. There are countless stars and probably many more planets in what we consider potentially habitable zones. I'd like to believe there is some form of life on another planet somewhere. If not now, then in the past or future. But the chances of us finding out for sure are minimal to say the least.
And, come to think of it, they'd probably give earth a wide berth when they saw the the human penchant for wars.
And, if you want to learn how to stop aliens abducting you then look here: http://www.stopabductions.com/ 
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