The Data Protection Commission (DPC) is working to investigate a Facebook data leak affecting up to 1.5 million people in Ireland.
Names, email addresses and phone numbers of one and a half million Irish people are now available online.
Additional information given by users to Facebook, such as locations and employers names, are also now in the public domain, as a result of the data leak affecting 530 million people globally.
It is believed the information was scrapped from the site back in 2018, before GDPR rules were introduced.
It is not believed the leak will affect people who use WhatsApp, which is owned by Facebook as the messaging platform provides end-to-end encryption.
In a statement, the DPC said: “A dataset, appearing to be sourced from Facebook, has appeared on a hacking website this weekend for free and contains records of 533 million individuals.
"A significant number of the users are EU users. Much of the data appears to been data scraped some time ago from Facebook public profiles."
The DPC said it had received "no proactive communication from Facebook" as it attempted over the weekend to establish the full facts and said it would communicate further facts as it receives information from Facebook.
