A photo posted early Wednesday by Randi Zuckerberg of the Zuckerberg family checking out Poke, Facebook's latest mobile app, was shared on Twitter, the Chicago Tribune reported.
Randi Zuckerberg was quick to tweet her anger at the photo being shared publicly.
"Not sure where you got this photo," she tweeted to Twitter user @cshweitz. "I posted it to friends only on FB. You re-posting it to Twitter is way uncool."
An apology by Callie Schweitzer, the Twitter user, was later accepted by Zuckerberg, who acknowledged Schweitzer probably saw the picture because Schweitzer is Facebook friends with another Zuckerberg sister, tagged in the photo.
Under Facebook's current privacy policies, tagged photos are visible to friends of every user in the photo, not just the friends of the user who posted it.
Randi Zuckerberg is not alone in being tripped up by Facebook's convoluted privacy settings, experts said, and some Facebook users were quick to wade in on the controversy.
"This is absolutely about privacy settings," a Facebook user responded to Randi Zuckerberg's tweet. "That person shouldn't have seen it. Your brother's site is doing this to us all!"