Facebook admitted 311,127 users in Australia were among up to 87 million users worldwide whose data was unknowingly shared with the agency.

The breach, which potentiallly affects up to one in 50 Facebook users in Australia, will be formally investigated by Australia’s privacy commissioner.

Acting privacy commissioner Angelene Falk has launched a formal investigation to consider whether Facebook has breached the Privacy Act, she said in a statement today.

Cambridge Analytica used the information to develop controversial tools for political campaigns, including Donald Trump’s 2016 run for US president.

Facebook’s announcement was substantially higher than the previous estimate of more than 50 million users being affected.

The social media group admitted the figure was based on its “best estimate” of the maximum number of accounts that installed Cambridge Analytica’s app, and the friends of those app users whose data may have also been shared.

“We do not know precisely what data the app shared with Cambridge Analytica or exactly how many people were impacted,” Chief Technology Officer Mike Schroepfer said in a statement.

While US users made up most of the 87 million people affected, the UK, Philippines and Indonesia each had more than one million accounts affected.

Australians made up one in every 250 accounts accessed.

Facebook has 15 million monthly active Australian users, Social Media News estimates.

The social media giant has previously argued the incident does not constitute a data breach as users signed up to the app.

“People knowingly provided their information, no systems were infiltrated, and no passwords or sensitive pieces of information were stolen or hacked,” Facebook vice-president Paul Grewal said in March.

– AAP