People can now enter their phone numbers into a website to see if they appeared in a recent Facebook data breach.
Details of more than 530 million people were leaked in a database online, largely consisting of mobile numbers.
People can use the Have I Been Pwned online tool to check if their numbers or emails were compromised.
Facebook says the data is from an “old” breach in 2019 but privacy watchdogs are now investigating.
Facebook said it had “found and fixed” the breach more than a year-and-a-half ago.
But the information has now been published for free in a hacking forum, making it widely available.
The database covers 533 million people in 106 countries, according to researchers analysing the data. That includes 11 million Facebook users in the UK, 30 million Americans and 7 million Australians.