Facebook is set to notify the millions of users whose data may have been leaked in the privacy breach scandal that has rocked the tech company.

The estimated 87 million people whose data might have been shared with political data-mining firm Cambridge Analytica, of which 300,000 are expected to be Australian will soon receive a message informing them of that fact. Any New Zealanders effected are also expected to be notified.

All 2.2 billion Facebook users will receive a notice on their feeds titled "Protecting Your Information." It will have a link to information on which Facebook apps they use and what information they have shared with those apps.

Cambridge Analytica allegedly used ill-gotten Facebook user data in its efforts to sway elections. The company says it only ever received data on 30 million users, reports News.com.au.

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Facebook has also announced it will require advertisers who want to run either political ads or so-called "issue ads" -which may not endorse a specific candidate or party but which discuss political topics- to verify themselves.

Facebook is working to strengthen its system ahead of this year's U.S. midterm elections and other elections around the world. The company has already required political ads to verify who is paying for them and where the advertiser is located. The requirement for issue ads is new.

In addition, Facebook says it will also require the administrators of pages with a "large number" of followers to verify their identities and addresses. The company did not specify what number of followers would trigger the requirement.

It comes as Facebook's Chief Operating Officer Sheryl Sandberg said Facebook should have conducted an audit after learning that a political consultancy improperly accessed user data nearly three years ago.

Sandberg told America's Today show that the company is now undertaking that audit.

Sandberg said that at the time, Facebook received legal assurances that Cambridge Analytica had deleted the improperly obtained information.

"What we didn't do is the next step of an audit and we're trying to that now," she said.

Facebook Founder and CEO Mark Zuckerberg's personal messages have got him into trouble before. Photo / AP
Facebook Founder and CEO Mark Zuckerberg's personal messages have got him into trouble before. Photo / AP

It comes amid reports Facebook has deleted messages that Mark Zuckerberg sent to others over fears the information would be leaked.

TechCrunch reports that three separate sources have revealed they had received messages from Zuckerberg that have now mysteriously disappeared from their Facebook inboxes.

However, their replies to his messages still remain.

Facebook confirmed that it had deleted these messages for security reasons.

"After Sony Pictures' emails were hacked in 2014 we made a number of changes to protect our executives' communications. These included limiting the retention period for Mark's messages in Messenger. We did so in full compliance with our legal obligations to preserve messages," the company said.

Facebook has never informed users that it had this sort of power, nor are regular users able to do the same thing. Users can only delete messages from their own inboxes.

None of Facebook's terms of service appear to give it the right to remove content from users' accounts unless it violates the company's community standards.

Zuckerberg's personal messages have come back to haunt him before. In 2010, Silicon Valley Insider published messages from a 19-year-old Zuckerberg to a friends just after he started his company, then called The Facebook, back in 2004.

"Yea so if you ever need info about anyone at harvard ... just ask ... I have over 4000 emails, pictures, addresses, sns" Zuckerberg wrote.

"What!? how'd you manage that one?" they asked.

"People just submitted it ... I don't know why ... they 'trust me' ... dumb f**ks" Zuckerberg replied.

Zuckerberg later told The New Yorker he regretted sending those messages.

"If you're going to go on to build a service that is influential and that a lot of people rely on, then you need to be mature, right? I think I've grown and learned a lot," he said.

It comes as Facebook reels from the data leak of at least 87 million users' information during the 2016 US election to Cambridge Analytica.

Zuckerberg will testify before US Congress this week on the leak and what he is doing to protect the information of users.

On Friday the Australian Privacy Commissioner launched an investigation into the scandal, and revealed around 300,000 Australians are likely to be affected.

The Office of the Australian Information Commissioner could impose new regulations and multimillion-dollar penalties on Facebook after launching an investigation into revelations it "improperly shared" the personal information of more than 311,000 Australians.

Australia's investigation will look into whether Facebook broke Australian privacy laws and "adequately notified" users that their information had been sold, but privacy experts warned it was a "David and Goliath battle" and could be hard to prove social media users hadn't accidentally consented to handing over their information.

Acting Privacy Commissioner Angelene Falk announced the Facebook investigation two weeks after requesting information about Australians' involvement in the Cambridge Analytica scandal.