The movie fictionalized much of Eric M. O'Neill's story. Among the changes made for the film: The real O'Neill knew going in that Robert Hanssen was the subject of a counterintelligence investigation. There was no cover story about sexual perversions, and no dramatic meeting where O'Neill learned the truth. There was no extensive contact outside the office between O'Neill and Hanssen as shown in the film (e.g. O'Neills visiting the Hanssens, Hanssens dropping by O'Neill's apartment); however, Hanssen did take O'Neill to church. The scene where Hanssen takes O'Neill out into the woods and drunkenly fires his pistol is fictional. Unlike in the movie, O'Neill never saw Hanssen after the arrest. While O'Neill did obtain Hanssen's PDA, he took it to FBI techs to download rather than downloading it himself.
In the hallway, we constantly see a poster with names and pictures of spies that have been caught, as well as short narratives of what their crimes were and how much time they're serving. These posters really exist in secure government facilities, and prominently displayed on all of them, since the events of this movie took place, is a photo of Robert Hanssen.
Robert Hanssen tells Eric O'Neill, "if I ever catch you in my office again, you're gonna be pissin' purple for a week." The real Robert Hanssen's undoing was a George S. Patton quote about "the purple-pissin' Japanese", a quote which Hanssen was fond of repeating. The FBI had paid a Russian agent $7 million for the KGB's file on the American mole - known to the KGB at the time only as Ramon Garcia. The file included a note of the mole about "purple-pissing Japanese" and Robert Hanssen became the prime suspect in the investigation. The FBI arrested Hanssen three months after receiving the file. The film concerns the last two months of the investigation.
In the film, Robert Hanssen has surreptitiously videotaped himself having sex with his wife and instructed Eric M. O'Neill to mail the tape to his friend James Hofsteller in Germany. Actually, Hanssen set up a closed-circuit camera and monitor (using equipment belonging to the FBI) so his friend, whose name is actually Jack Hoschouer, could watch during his visits to the Hanssens.
After the opening scene, code quickly flashes and is reduced to the movie title. The scrolling code is a Linux procedure that mounts (connects to) networked data sources such as Unix, Windows and Novell file systems.