A data leak posted online on Saturday includes some 1.4 million user accounts from Finland, according to the Finnish transport and communications agency Traficom.
Business Insider reported on Saturday that Alon Gal, of cybercrime intelligence firm Hudson Rock, discovered the data of some 533 million Facebook users on Saturday.
The data was first scraped in 2019, but was posted on a forum on Saturday making it freely available to anyone with basic data skills.
Traficom's Cyber Security Centre said the leak included data from some 1.4 million accounts linked to Finland. It includes phone numbers, Facebook profile IDs, birth dates and in some cases email addresses.
"According to publicly available information the attacker has exploited a now-fixed vulnerability to steal a list of phone numbers from Facebook and then used them to get more data from the profiles," said a statement on the centre's website.
"Although a phone number might have been hidden, it could now be available and linked to Facebook profiles."
A Facebook representative told Business Insider that the data was scraped in 2019. Alon Gal tweeted that the leak was exceptionally broad.
"This means that if you have a Facebook account, it is extremely likely the phone number used for the account was leaked," tweeted Gal.