This is one of my pet peeves as well. I learned several years ago that everyone is not your friend. I separate my friends in very controlled categories; very close/trustworthy/dependable/loyal and the second group are casual friends/acquaintances/social. After being stung many times I learned who can be trusted and who can't. When a person believes that they have a bunch of close friends they are really in for a big surprise. People love to gossip and use information about someone to gain importance to other people regardless of the damage it causes.
I don't tell anyone outside my close group anything. I am nice and friendly and enjoy being with them but there in an impenetrable wall around me.