" Behind the Facebook profile you’ve built for yourself is another one, a shadow profile, built from the inboxes and smartphones of other Facebook users. Contac

" Behind the Facebook profile you’ve built for yourself is another one, a shadow profile, built from the inboxes and smartphones of other Facebook users. Contact information you’ve never given the network gets associated with your account, making it easier for Facebook to more completely map your social connections. " Careful sharing your addressbooks... you may have non-personal (friends) contacts in there you may not wish Facebook to link to your profile and "People You May Know" suggestions