Do you remember the olden days of losing a phone? Crap! You lost all your contacts! What do you do? You probably didn't have a smartphone and you probably didn't sync your contacts, instead, you went to Facebook and told your friends to give you their numbers. Those phone numbers are still on Facebook.
Buzzfeed FWD looked at the ol' lost phone problem and found that countless Facebook Groups were created for the sole purpose of getting people's phone number back. It was simple, people invited all their friends to post their phone number to the Group so they could add to their new phone. The problem is that even though groups are defunct now, the posts of your phone number are still there. Even worse, none of the old groups' members (other than the creator) know about this, as they've been exorcised from the group long ago.
Which means, no one knows what graveyard post their phone numbers continue to live in. Which means, those numbers could be "harvested by nefarious individuals like text-message scammers and spammers". Which means, that's totally not cool. Read the whole report on FWD. [BuzzFeed FWD]