What are “unclean spirits?” Are they demons? Are they still around today?
God is Spirit
Jesus told the Samaritan Woman at the Well that, “God is spirit, and those who worship him must worship in spirit and truth” (John 4:24). Jesus is God, but Jesus came to be born in the flesh (John 1:14) to save that which is in the flesh (you and I). He divested Himself of the glory He had with the Father in heaven to humble Himself to the point of death on a cross (Phil 2:8). That’s what it took to save us, but we know that God has neither hands nor feet nor arms or legs, but is Spirit. Even though God says He watches over those who live in obedience and that Israel was the “apple of [His] eye” (Psalm 17:8; Zech 2:8), God is Spirit, and therefore, He has no eyes as we do. God has to use anthropomorphic language (to dumb it down for us), so that we can understand how God feels when He speaks about Himself in relation to us or to Israel.
Manifested in the Flesh
Only Jesus has manifested Himself in the flesh, but basically, God is Spirit, but God is also Creator, and He created the angels. Apparently the angels had freewill for a time because 1/3rd choose to follow Satan in his rebellion. These angles are also spirit, but they are created beings and not eternal ones. There was a time when Satan and the angels didn’t exist, but there has never been a time when God has not existed, nor will there ever be a time when God does not exist. He is the Self-Existent One…the “I AM” and needs no cause. Today there are holy angels that have chosen to live in obedience to God and are dispensed and dispersed whenever He wills, but these angels are also spirit. Occasionally, if it is God’s will, they are manifested as human beings, but that was only because it was God’s will. Holy angels never act independently of God’s will. That’s not true of the fallen ones (us), or the evil spirits that exist in the world today.
The Old Testament doesn’t precisely have the words “unclean spirits” in it, but there are dozens of references to the same thing. In 1 Samuel 16:14 we read that “the Spirit of the LORD departed from Saul, and a harmful spirit from the LORD tormented him.” Something I noticed is that the “harmful spirit” could not torment Saul until “the Spirit of the LORD departed from Saul,” meaning no believer can be possessed by Satan or demons. That’s because the Spirit of God that is in us is greater (God) than the unclean spirits in the world (1 John 4:4). The “harmful spirit” sent to Saul was nothing more than an unclean or demonic spirit, so unclean or demonic spirits have been in the world since man was created. There are ten occurrences of the words “unclean spirits” in the New Testament, and they all refer to demonic spirits or fallen angels. Referring to unclean spirits being cast out of a person, Jesus warned that “When the unclean spirit has gone out of a person, it passes through waterless places seeking rest, but finds none” (Mat 12:43), however, if that person returns to their previous evil wicked practices, then the unclean spirit “goes and brings with it seven other spirits more evil than itself, and they enter and dwell there, and the last state of that person is worse than the first. So also will it be with this evil generation” (Matt 12:45).
Jesus, as God, has authority over Satan and his demons. We read where Jesus shared this authority with His disciples. It says, “he called to him his twelve disciples and gave them authority over unclean spirits, to cast them out, and to heal every disease and every affliction” (Matt 10:1). When those in the synagogue saw Jesus cast out a powerful demon, they were astonished and ask, “What is this? A new teaching with authority! He commands even the unclean spirits, and they obey him” (Mark 1:27). Tragically, we often don’t recognize Jesus’ sovereignty and authority, but the demons always recognize it, and even acknowledge it publically. One example is “Whenever the unclean spirits saw him, they fell down before him and cried out, “You are the Son of God” (Mark 3:11). Even here Jesus rebuked them for it was not time for the world to know exactly Who He is (the Messiah and Savior), so they all acknowledged that Jesus is God. In fact, they had no choice but to do what the Lord said. A lot of people today say they believe in Jesus, but just to believe is not enough. James wrote, “You believe that God is one; you do well. Even the demons believe—and shudder” (James 2:19), so if it is only an intellectual knowledge of Jesus, you’re only qualified to be a demon, because the demons also believe and tremble, but they’re not saved. To know Jesus is not the essential question. The critical question is, “Does Jesus know you?” Many will claim they “know” Him on the Day of Judgment, but those same “many” will be turned away because Jesus did not know them (Mat 7:21-23). How tragic…and avoidable. If only they would have repented and trusted in Christ.
Not only are there unclean spirits or fallen angels, called demons, there are people who are influenced and in some cases, possessed by demons. The Apostle Paul knew all about unclean spirits, and he wrote that “even if our gospel is veiled, it is veiled to those who are perishing. In their case the god of this world has blinded the minds of the unbelievers, to keep them from seeing the light of the gospel of the glory of Christ, who is the image of God” (2 Cor 4:3-4). The enemy and his minions are trying to veil or cover up the gospel and present their own version of the gospel, which is no gospel at all. Demons probably know the Word of God better than we do, so they make great preachers, and we know that Satan’s ministers appear as angels of light (2 Cor 11:14), but the difference is they water down the gospel. They love to take texts out of context and create false pretexts. Cults are built on “proof texting” and one-verse theologies thrive in satanic or demonically influenced churches. That’s why we must put on the armor of God every day, “For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil in the heavenly places” (Eph 6:12). These are the unclean spirits at work today in the children of disobedience, making them follow the course of this world (Eph 2:2).
Here is some related reading for you: Does the Bible Say What the Devil, Satan or Demons Look Like? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.