It is important to note beforehand that demons, spirits, and devils have all different words in Hebrew, and thus should not be treated interchangeably, but as separate concepts/entities. Do realize that this question can be answered in great length, but for the sake of brevity we'll do what we can here. First off, there is the necessity to realize that an evil spirit might be evil when it comes to our human perspective because of the product or consequence we see of its presence or actions, but we must realize that according to The Bible, they have a boss, as can be seen in the book of I Sam. when it says, "God sent a melancholy(evil)spirit to torment King Saul. This brings us to the first answer to the question. People can get evil spirits when sent to them by God. I'm not here to answer why, just how. Secondary, spirits are attracted to human emotion. For example, if a person feels angry about something, spirits are capable of taking that emotion, and act like catalysts to increase its power and potency. Take the same example of King Saul, he was depressed and the spirit increased the power of such emotion into blinding homicidal rage towards David.
We could go on
an evil spirit
Good Spirit
An evil spirit's hammer and wrench are a ghoul's tools
Sightings - 1992 Evil Spirit was released on: USA: 1996
No, scientifically these are not recognised to exist so they can not be cured.
They thought that evil spirits made them ill.
To drive out an evil spirit.
Zero
The evil spirit to whom Faust sold his soul is named Mephistopheles.
The evil spirit took over the house.
What Evil spirit that likes to cause trouble for humans with o and I in the word
kain