In a privacy lapse, more than 400 million phone numbers linked to Facebook accounts were listed online according to media reports.
According to technology web site TechCrunch, the exposed server stored more than 419 million records of users from several databases in the US, Vietnam and Britain.
These databases had Facebook user IDs with unique digits of each account, profiles' phone numbers, listed according to gender and their geographical locations.
But as the server was not password protected, anyone could easily access the databases.
Facebook confirmed part of the report, saying that the number of accounts exposed so far was half of what was reported, adding that many of the entries were duplicates and the data was old.