Facebook's much derided privacy settings came back to bite the family of the site's founder on their festive behinds this Christmas.
Mark Zuckerberg's sister, Randi, posted a family picture of them all reacting to the social network's new "poke" app.
Callie Schweitzer, a marketing director at Vox Media, saw the picture in her Facebook feed and, thinking it was a public photo, reshared it on Twitter.
The image was actually only published on Randi's private network and Schweitzer could only see the pic because she is friends with Mark's other sister who was tagged in the photo.
Schweitzer deleted the photo after an angry Randi tweeted her disapproval, but not before sites such as Buzzfeed had guaranteed it went viral.
Despite a grovelling apology Randi continued, tweeting: "Digital etiquette: always ask permission before posting a friend's photo publicly. It's not about privacy settings, it's about human decency."
The irony of the sister of Mark Zuckerberg being caught out by the sites complex privacy settings appeared completely lost on her.