Do you think aliens in ufos have visited Earth? (And all things UFO)

I assume there is some form of life in other parts of the Universe, however, for that life to be intelligent and to exist in the same timeframe as us is a very small probability. Then, on top of that, they would have to be able to find us and not be noticed by us... nothing I have seen so far has convinced me that it has happened. Don't get me wrong, I certainly think it's possible for intelligent civilizations to exist elsewhere at some point in time, but I'm skeptical that they ever found there way here while we were here.