By "secrets" I mean any data you don't want known to the public. In a recent incident (via Schneier), that should include posting a selfie of yourself holding a winning betting ticket:
A woman has lost $825 she won betting on the 2015 Melbourne Cup after she posted a photo of herself holding the winning ticket on Facebook.
According to The Daily Mail, a woman named Chantelle placed a $20 bet on the 100-to-1 shot Prince of Penzance at this year’s Melbourne Cup, Australia’s most prestigious Thoroughbred horse race.
Chantelle believes that though her fingers were covering up part of the ticket’s barcode in her selfie, a “friend” on her profile might have used her photo and [another photo of the ticket] to piece together the complete barcode, run it through an automated machine, and claim the winnings themselves.
So, kudos to Chantelle for knowing not to post the entire barcode, but, um, maybe she shouldn't have posted any of it?