The sister of Facebook founder Mark Zuckerberg has been caught up in a Twitter debate after a private family photo posted to her brother's social media website ended up going public.

The picture intended for "friends only" was posted on Facebook by Randi, one of the internet entrepreneur's three sisters, and shows the Zuckerberg family in their kitchen excitedly reacting to the site's new Poke application.

Mark appears in the background of the photo looking puzzled and bashful by his family's excitement.  

The photo was then tweeted Wednesday by Callie Schweitzer, a director of marketing and projects at a Washington-based internet media company who has over 40,000 followers.  

Schweitzer tweeted "@randizuckerberg demonstrates family's response to Poke #GAH."

Randi,  Facebook's former marketing director, responded a short time later in the early hours of Wednesday: "@cschweitz not sure where you got this photo. I posted it to friends only on FB. You reposting it to Twitter is way uncool."

Schweitzer tweeted back apologizing and saying she subscribed to Randi's profile and it "seemed public" after showing up at the top of her Facebook newsfeed.

But Randi, who has over 1.4 million subscribers on Facebook, wasn't convinced and tweeted "@cschweitz I think you saw it b/c you're friends [with my] sister (tagged.) Thx for apology. I'm just sensitive to private photos becoming 'news.'"

Schweitzer later deleted the photo from Twitter and Zuckerberg offered her own piece of friendly advice.

"Digital etiquette: always ask permission before posting a friend's photo publicly," she tweeted a couple of hours later. "It's not about privacy settings, it's about human decency."

Revisions to Facebook privacy settings

But Randi's comments sparked sharp reactions from people who thought the issue wasn't about etiquette, but rather Facebook's often changing and confusing privacy settings.

Eva Galperin of the Electronic Frontier Foundation, a privacy advocacy group in San Francisco, said the privacy settings remain confusing to most people and sometimes the consequences of fumbling them can be serious.

"Even Randi Zuckerberg can get it wrong. That's an illustration of how confusing they can be," she said.

The Menlo Park, Calif., company recently announced it will start rolling out revisions to its privacy settings over the next few weeks with the aim of making it easier for users to navigate them.

The most visible change will be a new privacy shortcuts section that appears as a tiny lock at the top right of news feeds. This feature offers a drop-down box where users can get answers to common questions such as "Who can see my stuff?"

Last month, Facebook dropped its system that allowed the over one billion users of the social media site to vote and comment on proposed changes to privacy policy.

With files from the Associated Press