DH and I went to dinner with two of his (Christian) coworkers last night. DH told us about working with a doctor who has a book about differentiating between a psychotic episode and demomic possession. Among the four of us, there were 3 different demoninations represented, and we all had different thoughts. DH believes that demons can possess people, one of the girls believes that demons exist but can't possess people, I believe that demons cannot possess Christians because of our Redemption through Christ, and the other girl wasn't sure and texted her BF because he is better at remembering what is where in the Bible. The BF responded that demons exist - they're in the NT. He texted, so we didn't get more of an explanation.
SO, I know Jesus cast out the Legion in the Gospel of Mark, and I think in Luke (maybe John?) there's another passage about him casting out demons. Are demons ever mentioned in the OT? I would think they would be since they were obviously a problem for people in the NT, but I do not know of any mention of them in the OT. Are we all saved from demons because of Christ? Just Christians?