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Some of the most trafficked websites for watching videos have begun deploying systems that remove and automatically block extremist content, Reuters reported on Saturday. These new restrictions on videos were enacted amidst concerns expressed by European leaders and President Barack Obama over online radicalization following an uptick in terror attacks in Europe and the United States.

According to Reuter’s sources, who are familiar with the process, Youtube, Facebook and Google have all been quietly implementing the censorial technology, which was originally developed to wipe copy-righted material from video sites.

The technology can also identify reposts of banned content. Because the system operates by searching for a unique digital fingerprint automatically assigned to certain videos by internet companies, it would not be able to automatically block a kind of video that has never been seen before.

Reuters reports that the two sources for its story, “would not say how videos in the databases were initially identified as extremist.”

Internet companies including Youtube, Facebook and Twitter met (virtually) in late April to discuss implementing content-blocking systems for extremist content.

Until now, most internet companies have mainly relied on users to flag inappropriate content that violate their terms of service.

Not all internet companies are on board with these new contont-managment tools, or at least not yet. A spokesperson from Twitter told Reuters that the company has “not yet taken a position” on automated policing of extremist content.