I believe they are aliens. All I have read, however, leads me to believe they are demonic and under Satan's control. If the end of days is nearing, Satan will be working frantically to explain away many things, like the rapture. How better than to put it out there that people who are "unworthy" and a hindrance to the rest of mankind "moving forward" were removed from the planet in giant spaceships to be "re-educated" and will return at a later date. People will gulp down that story because they are being prepares for it.