Facebook has confirmed that millions of user phone numbers were stored on a server without password protection.
TechCrunch claimed the social media giant left around 419 million data records on an unprotected online server.
Of that figure, around 18 million UK phone numbers are said to have been left exposed.
A total of 133 million records for US users, and a further 50 million records for users in Vietnam, are said to be among the data.
Read more Yahoo News UK
An unspecified number of records also held additional details, such as the user’s name, gender and location by country.
It is also claimed a user’s unique Facebook ID was stored next to their phone number.
Facebook has confirmed reports around the unprotected server.
However, it said the total number is likely to be around 210 million - half of the figure cited in the report - due to duplicate entries.
The social media site said the online data has now been removed, and said there was “no evidence” that Facebook user accounts had been compromised.
A spokeswoman said: “This dataset is old and appears to have information obtained before we made changes last year to remove people’s ability to find others using their phone numbers,”
“The dataset has been taken down and we have seen no evidence that Facebook accounts were compromised.”
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The social media site has been the subject of scrutiny since the Cambridge Analytica scandal.
The two companies harvested the personal details of millions of peoples' profiles without consent.
In July, the Federal Trade Commission agreed a settlement with Facebook, which included a £4 billion fine plus compulsory audits into the business to ensure privacy and data protection is in place.
Recently, it was claimed Facebook staff used secret tools called Stormchaser and Night’s Watch to track down hoaxes and fake news - about Facebook.