Think Facebook knows a lot about you from all the information you enter into the site? Well it now appears that Facebook may soon know a lot more than you thought. In the past few days Facebook added a new feature on the Friends page which enables you to view “Friends without Facebook Profiles”. I checked it out and Facebook seems to think that none of my friends aren’t on Facebook. While inaccurate, I’m not sure if I am relieved to see that Facebook doesn’t know which friends aren’t registered.
So how does Facebook mysteriously determine which of your friends aren’t on the site? One theory I have is related to photo tagging. Frequently, users will tag other people in photographs that haven’t registered for the site. My guess is that if you end up in enough photos with that unregistered user, they will be added as a friend not on Facebook. Another theory I have is related to Facebook’s new Facebook Connect feature.
When you login to a site outside of Facebook with Facebook Connect, the external website has the ability to pass back all of your friends that you are connected with on that site. In turn they pass back all of the email addresses and names of your friends. If that email address hasn’t been registered on Facebook they will show up in your friends list as “Friends without Facebook Profiles.” Do you have any other theories about how this shows up?