The personal data of more than 500 million Facebook users has been shared on an online hacking forum.
The huge data leak involves the phone numbers and personal data of 533 million accounts from 106 countries.
Around 11 million users have been affected in the UK, compared with 32 million in the US and six million in India - while many accounts in Ireland were also hit.
The details that have been leaked include Facebook IDs, birthdates, names, locations and in some cases email addresses.
Facebook told Business Insider that data was stolen as a result of a security issue that the company patched in 2019.
The 'data set' was shared on a hacking forum on Saturday.
But there's an easy way to check if you've been affected.
If you enter your name, phone number or email address into https://haveibeenpwned.com/, you'll be able to find out whether your account was part of the data leak.
Alon Gal, the chief technology officer of the cybercrime intelligence firm Hudson Rock, spotted the republished data on the hacker forum.
He told Business Insider:
"A database of that size containing the private information such as phone numbers of a lot of Facebook's users would certainly lead to bad actors taking advantage of the data to perform social-engineering attacks [or] hacking attempts."
A spokesman for Facebook told Bloomberg:
“This is old data that was previously reported on in 2019.
“We found and fixed this issue in August 2019.”
