I have been reading this for a while and i have to agree with the scripture a Christian walking with the spirit or light within him cannot be possessed but only influenced but i think a lot of people are getting confused because they have seen Christians being possessed which i have also and by possessed i mean completely taken over.
I was at a youth bible camp several years ago and we were in a church service praying at the front, one of my friends fell over, no big deal we sometimes see this when people are hit with the holy spirit powerfully, so we lifted him back up, it happened again we stood him up again, it happened one more time so we decided to leave him on the ground, he then started to twitch a little, and then suddenly opened his eyes very wide and sat up(he was on his back) very quickly as if he just awoke and was startled, he then looked around him at people praying and started freaking out and he scurried back towards the chairs as if he was afraid and kicking his feet to scoot himself back with inhuman speed as he neared the chairs(all of them being empty) they all blasted back into a large semi circle without touching any of them and without flipping over.
We then sat him on a chair and gathered around him to pray, he was twitching a little while we were praying then his head shot up when someone mentioned the name of Jesus out loud he stared right into the eyes of one of the pastors and in a very non human voice said "i hate Jesus and i hate you(talking to the pastor)" after a while we cast it out
Now this is a very clear case of total controlling possession of a "christian" and for me it was God that confirmed it to be genuine as while we were praying for him God spoke to me and told me to lay my hand on his head, i was young and scared so i hesitated it wasnt a minute later when the pastor mentioned above turned to everyone and said God is telling me that we all need to lay our hands on his head, needless to say my hand was on his head before he even finished the sentence and it was after that when we rebuked the demon and got through to the person who then repeated the name of Jesus casting the demon out.
So again full possession not just influence of a "christian" but here is where i think the confusion lies, if that christian has turned from god in this case listening to a lot of well demonic music and not praying ect. in which case he tied up his own strong man and extinguished whatever light he had in him allowing the darkness to come in, Isaiah 59:2 "But your iniquities have separated between you and your God, and your sins have hid his face from you, that he will not hear." So he extinguished his light allowing darkness to enter and allowing to be possessed because he had turned from God and was Backslidden but to many who did not know he was still a Christian in their eyes therefore the appearance of a Christian being possessed.
So please do not be confused when the scripture says a christian with the holy spirit and Jesus inside him cannot be possessed then they can NOT be possessed but when a christian has extinguished his light and effectively shut Jesus and the Holy spirit out of themselves perhaps without even knowing it, Matthew 7:22-23<sup class="versenum" id="en-NIV-23339"> "22</sup> Many will say to me on that day, ‘Lord, Lord, did we not prophesy in your name and in your name drive out demons and in your name perform many miracles?’ <sup class="versenum" id="en-NIV-23340">23</sup> Then I will tell them plainly, ‘I never knew you. Away from me, you evildoers!’" then yes it becomes possible for a "christian" to become possessed, hope that clears up a little confusion God Bless