http://www.khouse.org/articles/1997/22/
 
Hi Gus,
 
Follow this link to a study by Chuck Missler on your exact subject. He has written a book called "Return of the Nephilim" and presents evidence that the same kind of mixing between fallen angel and human seed that took place in Noah's day to produce giants or Nephilim is prophesied to be going on in the last days. You are correct that the UFO and alien phenomenon is likely the fulfilment of these kinds of activities in our day.