"For false Christs and false prophets will appear and perform signs and miracles to deceive the elect -- if that were possible." -Mark 13:22
This is true today.  There are many religions that are infiltrating the churches that have renamed their demons "Jesus," "Christ," "God," "Jehovah" and "the Spirit."  They claim "salvation" to be merely enlightenment, advancing in karma, etc.  There are people with spirits of divination coming into the churches able to give accurate information, using Christian jargon.  Revelations 2:20 refers to such a one. 

'They are the kind who worm their way into homes and gain control over weak-willed women, who are loaded down with sins and are swayed by all kinds of evil desires, always learning but never able to acknowledge the truth." -2 Tim 3:6,7  Don't get smug and think this is only true of women!  And it is also true of churches!  You would be shocked at how much the members of your church are or have been involved in occult practices.  The last part of the verse speaks of someone with much book-learning but no divine guidance to detect evil.

Unfortunately, the typical Sunday morning service leaves the church wide open for these agents of the devil.  The bigger the church, the greater the opportunity for Satan's agents to remain anonymous.  They can come in, practice a little witchcraft in the pew and mess up a good service.  They can join the church and use witchcraft to get promoted to prominent positions.  And they do.

I was demonized by a man in the pew next to me at the passing of the peace thirty years ago.  He said, "Here, let me pray for you," and plopped a hand on my shoulder.  I let him do it, not wanting to create a scene.  I only figured out what was wrong when I had a poltergeist (knocking ghost) manifest in the wall next to my bed.  Later, after I cast out the demons out of me and him, I found out he had been going from church to church doing this for YEARS.  Nobody had ever caught him & stopped him.  This website is because of that man.

One important way of dealing with them is to quietly deliver the entire congregation and any charmed objects that have affected them, using the general cleanup sheet.  Wait for ten minutes, to catch the late-comers, as well.  I do it in the sound booth, so nobody hears.  This gets most of them.  It also cleans up any occult damage they were doing.  The agents usually don't come back.

I've also had covens lob in curses to whoever is in the local churches.  One time, we had an acolyte pass out on stage.  911 was called.  they were slow in getting to us, because a church up the road had an acolyte pass out on stage at the same time -- and they were a hair quicker in calling 911.  Nothing was ever found wrong with either acolyte.  I deliver anyone who has worked or conspired against my church over the last two months.

It is very important that all hiring and promotions be done with simultaneous prayer coverage.  It is also important to have all people joining the church or being promoted to make a special affirmation:  "Jesus Christ of Nazareth, the Son of Jehovah, is my only savior and master."  If they say a substitute statement, they must come back to this specific affirmation.  If they get belligerent, they must come back to this specific affirmation.  Three tries, you're out.  This gets most of them.