What is the Spirit of Anti-Christ?

"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." (1 John 4:3 KJV) 

"Little children, it is the last time: and as ye have heard that antichrist shall come, even now are there many antichrists; whereby we know that it is the last time. They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us." (1 John 2:18-19 KJV) 

"I rejoiced greatly that I found of thy children walking in truth, as we have received a commandment from the Father. And now I beseech thee, lady, not as though I wrote a new commandment unto thee, but that which we had from the beginning, that we love one another. And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it. For many deceivers are entered into the world, who confess not that Jesus Christ is come in the flesh. This is a deceiver and an antichrist. Look to yourselves, that we lose not those things which we have wrought, but that we receive a full reward. Whosoever transgresseth, and abideth not in the doctrine of Christ, hath not God. He that abideth in the doctrine of Christ, he hath both the Father and the Son. If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed: For he that biddeth him God speed is partaker of his evil deeds." (2 John 1:4-11 KJV) 

Antiochus IV Epiphanes (“God Manifest”) - Daniel 8:9-14; 1 Ma 1:10; Daniel 11:21-34; 1 Ma 1

2 Thessalonians 2:1-12; 1 John 2:1-6; Daniel 7:25