This is a simple question. With no simple answer. Currently there are no evidence what so ever that aliens have ever visited planet Earth. But given how primitive human civilization is. It is not hard to imagine that aliens going past our solar system to ignore us, or just take long range scans. Be that from far away from the Earth or in a high orbit above the Earth where we can not detect them.
But as mysteries goes. This one is going to be solved one day. I not know yet if I am going to see that day. But one can hope do so.