The leak includes personal information on 533 million Facebook users, such as phone numbers, Facebook IDs, full names, locations, birth dates, bios and in some cases email addresses, Business Insider reported.

“This is old data that was previously reported on in 2019,” a Facebook spokesperson wrote in an email statement. “We found and fixed this issue in August 2019.”

At the time, the company addressed a flaw in its technology that allowed the information to leak out. However, once such data escapes from Facebook’s network, the company has limited power to stop it from spreading online.

Alon Gal, chief technology officer of cybercrime intelligence firm Hudson Rock, discovered the data again on Saturday.

Databases, especially if they are large or rare, aren’t often shared widely right away because “the people who hold it will attempt to monetize it for as long as they can,” Gal said in a message on Twitter. “The process sometimes takes years, sometimes days, but eventually all private databases leak if they were sold around.”

Data leaks threaten to undermine Facebook’s business model of gathering a large amount of personal information and using that to sell targeted ads.

The information is available for free on a hacking forum, making it widely accessible to anyone with rudimentary data skills, Business Insider said. The publication verified several records by matching known Facebook users’ phone numbers with the IDs listed, and confirmed other records by testing email addresses from the data set in Facebook’s password reset feature, which can be used to partially reveal a user’s phone number.