Up to 40 staff at Dublin's Facebook headquarters may have had their personal details leaked to terrorists according to the Irish Independent.
The breach is believed to have affected people who monitor content from the social media site including terrorist propaganda and hate speech. Over 1,000 people may have been affected worlwide. Gardaí are investigating the situation here in Ireland.
A spokesperson said:
"Last year, we learned that the names of certain people who work for Facebook to enforce our policies could have been viewed by a specific set of group admins within their admin activity log.
"As soon as we learned about this issue, we fixed it and began a thorough investigation to learn as much as possible about what happened.
"This included determining exactly which names were possibly viewed and by whom, as well as an assessment of the risk to the affected person."