Google, Facebook, Twitter and Microsoft have pledged to work together to identify and remove extremist content on their platforms through an information-sharing initiative. Earlier this year Hany Farid, the computer scientist who helped develop PhotoDNA, proposed a sister program for extremist content. He teamed up with the Counter Extremism Project to develop a system that could proactively flag extremist photos, videos and audio clips as they are posted online. “There needs to be complete transparency over how material makes it into this hashing database and you want people who have expertise in extremist content making sure it’s up to date," he said. “What we want is to eliminate this global megaphone that social media gives to groups like Isis. This doesn’t get done by writing a press release.”