When Mark Zuckerberg's sister fell foul of Facebook's privacy settings...

The Zuckerberg family pose, with Mark Zuckeberg at the back, that found its way on to Twitter

Even a Zuckerberg can’t navigate Facebook’s privacy settings - or so it would seem after Randi, big sister to the social network’s co-founder Mark and the website’s ex-marketing director, shared a family photo with her Facebook friends only to find it floating freely in the open waters of the internet.

Like so many of the network’s billion-plus users, Ms Zuckerberg probably thought nothing of posting the snap on her brother’s website. It showed a assortment of Zuckerbergs in a kitchen with exaggerated expressions on their faces as they toyed with what was reported to be Facebook’s new Poke smartphone app. The billionaire sibling was in the background, looking somewhat embarrassed by his family’s antics.

But much to Ms Zuckerberg’s chagrin, what was meant to be a private post intended for her friends ended up on Twitter when it was posted on the micro-blogging site by one Callie Schweitzer, a New York City based marketing executive at Vox Media, who saw it in her Facebook news feed. Although she is not one of Ms Zuckerberg’s friends, Ms Schweitzer, it turned out, is an online buddy of one of other family members in the photo. When said member was 'tagged' - Facebook parlance for identifying people in an image by linking to their profiles - the picture, though private, popped up in Ms Schweitzer’s feed, making her think it was public.

“Not sure where you got this photo,” Ms Zuckerberg initially said in a tweet directed at Ms Schweitzer, who as of yesterday had more than 40,000 followers on the site. “I posted it only to friends on FB. You reposting it on Twitter is way uncool.”

The Twitter back and forth has since been taken down, but according to excerpts doing the rounds online, Ms Schweitzer responded with an apology, saying she was “genuinely sorry but it came up in my feed and seemed public.”

The digital penny seems to have dropped when the link became apparent. “I think you saw it [because] you're friends [with] my sister (tagged),” Mr Zuckerberg is reported to have said. “Thx for apology. I’m just sensitive to private photos becoming ‘news.’”

Though swiftly resolved the curious case of the Zuckerberg snap was seized upon by critics of Facebook’s privacy settings, which are routinely slammed for their complexity. @Spinchange, a Twitter user who responded to one of Ms Zuckerberg’s tweets claiming that the confusion wasn’t because of the site’s privacy norms but about “human decency”, said: “[This] is absolutely about privacy settings. That person should’t have seen it. Your brother’s site is doing this to us all!” Another user, @AileneZange, said: “We’ve all been dealing with loss of privacy in Facebook, now she feels what we all do everyday.”