Centralized social networks [ can learn a lot about people that don't directly give them data ]( http://www.wired.com/2014/10/privacy-friendster/ ) , through what others say about them and even who knows them. In other words, you should insist that your friends not mention you by name or email address in anything they post on centralized social networks. I think this applies to gmail as well.
Ссылка: https://stallman.org/archives/2014-jul-oct.html#14_October_2014_%28Centralized_social_networks%29