: Many profile "trackers" collect your device info and app activity, often sharing it with third parties for advertising or more nefarious purposes. Legitimate Ways to Interact with Private Profiles
Never enter your Facebook credentials into any third-party app or website claiming to offer profiling services. facebook private profile viewer by istaunch portable
If you share mutual connections, you may be able to see photos or posts that the target has tagged your mutual friends in, depending on their custom audience settings. : Many profile "trackers" collect your device info