Facebook CEO Mark Zuckerberg's cell phone number is among the leaked personal data from 553 million users of the site posted online by hackers.
Zuckerberg's name, location and marriage information, date of birth and Facebook user ID were among the trove of stolen personal data published on a hacker forum on Saturday, cyber researcher Dave Walker confirmed.
Facebook co-founders Chris Hughes and Dustin Moskovitz also had similar personal details included in the leaked data.
A Facebook spokesman said in a statement to DailyMail.com: 'This is old data that was previously reported on in 2019. We found and fixed this issue in August 2019.'
The database appears to be the same set of numbers circulating in hacker circles at least since January, according to Alon Gal, co-founder of Israeli cybercrime intelligence firm Hudson Rock.
That data had been sold and resold among cybercriminals for some time, but Saturday's leak on the hacker forum now makes it available essentially for free.
Personal information from users around the world is being offered for a few euros' worth of digital credit on a well-known site for digital hackers and Gal said he had verified the authenticity of the data.
Other journalists say they have also been able to match known phone numbers to the details in the data dump.
An attempt by Reuters to reach the leaker over the messaging service Telegram was not immediately successful.
Facebook says that the leak is believed to stem from an issue with the contact importer, which allowed people to find their friends through their phone numbers, and that the weakness was found and fixed in 2018.
Gal told Reuters that Facebook users should be alert to 'social engineering attacks' by people who may have obtained their phone numbers or other private data in the coming months.
In 2019, phone numbers linked to more than 400 million Facebook accounts were posted online.
According to TechCrunch, 133 million US accounts, more than 50 million in Vietnam, and 18 million in Britain were among 419 million records left in an open online server that was not secured with a password.