Looks like even the Zuckerbergs aren't completely clear on how Facebook's privacy settings work.
Facebook's privacy settings are always changing. Though the company likely thinks its settings are as clear and concise as possible, the truth is that many users find it hard to get their heads around the constantly evolving settings. In fact, even Mark Zuckerberg's own sister has trouble with the social network's complex privacy settings.
Over the holidays, Randi Zuckerberg posted a photo of herself and her family to her Facebook. One of her subscribers, Callie Schweitzer, saw the photo and tweeted it to her followers. However, it seems the photo wasn't actually public. Randi posted it to her Facebook and set the visibility to 'Friends Only.' Randi explained this Schweitzer, and said it was 'way uncool' of her to tweet a private photo. Callie shot back that the photo showed up on the top of her news feed and so she assumed it had been shared publicly because she isn't friends with Randi Zuckerberg and only subscribes to her public updates.
So what happened? Randi's sister was tagged in the photo and is friends with Callie Schweitzer on Facebook. Because Facebook's very granular privacy settings include options for sharing your tagged photos with your friends, Randi's photo was made visible to her sister's friends. Perhaps her brother Mark, also pictured in the photo, was the one who cleared up the situation?