The personal details of 100 million Facebook users have been published on the internet by a British security consultant.
Ron Bowles used a piece of code to scan Facebook profiles, collecting data not hidden by the user's privacy settings.
The list, which has been shared as a downloadable file, contains the URL of every searchable Facebook user's profile, their name and unique ID.
Mr Bowles said he published the data to highlight privacy issues and the file has spread rapidly across the net.
Facebook says it was already public information.
Earlier this year, there were protests from users of the site over the complexity of Facebook's privacy settings.
As a result, the site rolled out simplified privacy controls for its 500 million users.