The move is a major step forward for internet companies that are eager to eradicate violent propaganda from their sites and are under pressure to do so from governments around the world as attacks by extremists proliferate, from Syria to Belgium and the United States.
YouTube and Facebook are among the sites deploying systems to block or rapidly take down Islamic State videos and other similar material, the sources said.
The technology was originally developed to identify and remove copyright-protected content on video sites. It looks for “hashes,” a type of unique digital fingerprint that internet companies automatically assign to specific videos, allowing all content with matching fingerprints to be removed rapidly.
Such a system would catch attempts to repost content already identified as unacceptable, but would not automatically block videos that have not been seen before.
The companies would not confirm that they are using the method or talk about how it might be employed, but numerous people familiar with the technology said that posted videos could be checked against a database of banned content to identify new postings of, say, a beheading or a lecture inciting violence.
The two sources would not discuss how much human work goes into reviewing videos identified as matches or near-matches by the technology. They also would not say how videos in the databases were initially identified as extremist.
Use of the new technology is likely to be refined over time as internet companies continue to discuss the issue internally and with competitors and other interested parties.
In late April, amid pressure from US President Barack Obama and other US and European leaders concerned about online radicalization, internet companies including Alphabet Inc’s YouTube, Twitter Inc, Facebook Inc and CloudFlare held a call to discuss options, including a content-blocking system put forward by the private Counter Extremism Project, according to one person on the call and three who were briefed on what was discussed.
The discussions underscored the central but difficult role some of the world’s most influential companies now play in addressing issues such as terrorism, free speech and the lines between government and corporate authority.
None of the companies at this point has embraced the anti-extremist group’s system, and they have typically been wary of outside intervention in how their sites should be policed.
“It’s a little bit different than copyright or child pornography, where things are very clearly illegal,” said Seamus Hughes, deputy director of George Washington University’s Program on Extremism.
Extremist content exists on a spectrum, Hughes said, and different web companies draw the line in different places.
Most have relied until now mainly on users to flag content that violates their terms of service, and many still do. Flagged material is then individually reviewed by human editors who delete postings found to be in violation.
The companies now using automation are not publicly discussing it, two sources said, in part out of concern that terrorists might learn how to manipulate their systems or that repressive regime might insist the technology be used to censor opponents.
“There’s no upside in these companies talking about it,” said Matthew Prince, chief executive of content distribution company CloudFlare. “Why would they brag about censorship?”
The two people familiar with the still-evolving industry practice confirmed it to Reuters after the Counter Extremism Project publicly described its content-blocking system for the first time last week and urged the big internet companies to adopt it.