1 John 4:1-4:

Beloved, believe not every spirit, but try the spirits whether they are of God: because many false prophets are gone out into the world.
Hereby know ye the Spirit of God: Every spirit that confesseth that Jesus Christ is come in the flesh is of God:
And every spirit that confesseth not that Jesus Christ is come in the flesh is not of God: and this is that spirit of antichrist, whereof ye have heard that it should come; and even now already is it in the world.
Ye are of God, little children, and have overcome them: because greater is he that is in you, than he that is in the world.

Notes on 1 John 4:1-4:

You have already overcome antichrist spirits!  Therefore, you do not have to engage in the kind of bogus “spiritual warfare” that tries to “defeat” them.  Jesus already defeated them for you.  Why should you fear evil spirits when you have already overcome them?

Someone (or something) can only confess that Jesus Christ has come in the flesh if he believes that (1) Jesus pre-existed before He was conceived and born on the earth (2) Jesus came to earth as a real Man, not as God in a man costume.  Anyone who does not believe these things is of the antichrist and should not be a source of your instruction.

See also:

How to Deal with the Devil
How NOT to Deal with the Devil
Who You Are and What You Have
The Kingdom of God Is Here NOW
Sickness Is the Power of the Devil
What Mark 11:22 Really Means
What Romans 8:11 Really Means
Can Satan Heal?
How Can I Know That It’s God and Not the Devil Doing the Healing?
Does a Serious Sickness Attack Prove That a Major Breakthrough Is Just Ahead?
Should We Plead the Blood When Dealing with Demons?
Can I Cast a Demon out of a “Haunted” Location?
Objection: “Divine” Healings Today Are the Prophesied Lying Signs and Wonders of the Antichrist
Objection: The “Word of Faith” Movement Is a Cult