They prompt you to download "required verification packages" or software extensions that infect your device.
Once on the fake page (disguised to look like iStaunch), you see a fake loading bar and a message: "Profile decrypted. 86% complete. To prove you are human, complete one offer." facebook private profile viewer by istaunch
Stay safe, respect privacy, and remember: If someone wanted you to see their profile, they would have added you as a friend. They prompt you to download "required verification packages"