More than 1000 young people in Denmark are facing charges for distributing sexually explicit material of minors, after Facebook notified authorities of the activity.
They are accused of using the social media site's Messenger app to share around a video clip of two 15 year olds having sex.
Fifteen is the age of consent in Denmark but police have said that sharing the footage could be classified as distributing child pornography.
Inspector Lau Thygesen from Denmark's North Zealand Police said in a statement that the videos were shared "across the country" in autumn last year and the case is "very large and complex".
"We have taken the case very seriously as it has major implications for those involved when such material is spread."