More than a third of people in the U.S. believe aliens exist -- and more than 10 percent of the population believes they have seen an alien ship in the sky. The study from National Geographic Channel found that 80 million Americans -- or 36 percent -- are certain alien spaceship exist, and of those who believe, 79 percent are convinced the White House has kept information about other lifeforms a secret. The study also found that if an alien knocked on the door, 22 percent of respondents would try to befriend the alien, 15 percent would run away, 13 percent would lock their doors, and, only 2 percent would try to inflict bodily harm. Furthermore, 55 percent believe there are real-life Men in Black-style agents who threaten people who spot UFOs.