The Bible, however, makes no distinction between magic that is good and magic that is evil. In the Law given to Moses, God made his position quite clear. He said: “You must not practice magic.” (Leviticus 19:26) We also read: “There should not be found in you . . . a practicer of magic or anyone who looks for omens or a sorcerer, or one who binds others with a spell or anyone who consults a spirit medium.”—Deuteronomy 18:10, 11. Evil spirits do exist. In one essay a promoter of witchcraft warns: “The Shadows are out there: They exist, in the invisible world that parallels our own, living creatures. . . . The terms ‘Imp’, ‘Evil Spirit’ and ‘Demon’ are fairly accurate. They are very strong. . . . The most intelligent variety . . . are capable (if someone is helpful enough to open a doorway for them) of entering our world. . . . They can enter your body . . . , even asserting a degree of control over you. Yes, this is exactly like the old stories of Demon possession.”

http://www.watchtower.org/e/20000401/article_02.htm