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It is likely just a hyperlink, you didnt have to give your facebook credentials to log in. It was just an option.

If you want privacy, get Wickr or Bleep messenging services.

Wick is better by the fact its more developed and Bleep is more anonymous because youre using DHT Nodes, which are a state of the art peer to peer file sharong network feature I have to read more about.

www.wickr.com

www.bleep.pm