EWTN Catholic Q&A
Question from anon on 01-15-2013:

Are the "ghosts" that people are experiencing in some homes really evil spirits masquarading as people that lived and/or died in such house? I can't imagine God allowing someone from heaven to haunt a house. So if anything paranormal is going on, wouldn't it be done by evil spirits?

Answer by Fr. John Echert on 01-16-2013:

We do know that some/many demons are allowed to roam the Earth, until the return of Christ and the end of time. Whether or not the souls of the dead are ever allowed interaction in such a manner I cannot say and hesitate to speculate. When there is a question of a home or building having possible preternatural activity within it, we typically use exorcism prayers, which are directed at demons. By the way, priests are allowed to exoricise buildings without permission, but not persons.

God bless

Father Echert