Poltergeist is a supernatural-horror film released in 1982 and was directed by Tobe Hooper and it also stared Craig T. Nelson and Heather O'Rourke.
During the investigation of Lauren Kyte, Mulder suggests to Scully that Kyte was being followed by Howard Graves in the form of a poltergeist. After Mulder's theory, Scully replied "They're here", the infamous quote and tagline of the film Poltergeist. (TXF: "Shadows")