I go back and forth on this issue. Aside from no hard proof, I do have a hard time beleving that all these governments have been involved in this for so many years, and managed to keep it a secret. As the saying goes, the more people you have involved in a conspiracy, the less likely that conspiracy is real. Especially with how incompetent our gov't is. In this day and age, seems like somebody should've even hacked info on ET's.
I don't doubt that there are NHI civilizations. But even as vast as the universe is, I don't think its a slam dunk. Prof. Brian Cox thinks that there are probably only one or two intelligent civilizations at one time. Due to the probability that, for one, the more advanced a civilization becomes, the more likely it is to wipe itself out. Of course that assumption is faulty because its based on our own hubris. But for another, the circumstances that had to happen for us to exist are extremely lucky and probably not something that you will come across often in the universe. Doesn't even matter where situated in our solar system. Look at Jupiter and/or Saturn. If not for Jupiter and/or Saturn being in the right place, we probably wouldn't be here.