Demons are fallen angels and servants of the Great Deceiver, Satan. They appear to man as ghosts, lost souls, wandering spirits and more malarky.
Demons are attracted to people that refuse God and Jesus Christ. Satan and his followers love buddhists, followers of mohammed, and all religions that teach false doctrines. Satan created these lies and these false religions.
Those shivers you feel sometimes, the ones that scare you, are demon-driven.
Read the New Testament and you'll find when Jesus started teaching, He began healing people of their hurts, lamenes, blindness, and leprosy. He also began ousting demons from humans. Lots of demons from humans all over the Holy land. It appears many humans were possessed back then.
What's different today? Where are the demon-possessed humans? Two thousand years ago there weren't many humans on this planet, but plenty of demons. Today very few people know that many times many are truly possessed by one demon. Satan is using his forces wisely. In this age of mass misinformation, and odd beliefs, Satan only needs to use one demon to possess a human.