alien is just a another life form in the universe...
i think human technology is still thousand years away for travelling beyond solar system....
during these gap, if we encounter any alien on earth it is definitely a far more advanced alien community...
and history taught us that the 'founder' is always hostile...
they may be civilized but their conquest is always with own agenda...
i just hope that one day human will discover alien in some other planet and not vice versa....