Facebook, Microsoft, Twitter and YouTube, which is owned by Google, have announced they are going to work together to identify extremist content. Hany Farid helped to build that technology. He's a computer scientist at Dartmouth and an advisor to the Counter Extremism Project. The nonprofit's been trying to get the internet companies to take action. And now, finally, Farid notes, they are changing their tune. "For years, they have said that this is technologically not feasible. That was absolutely not true. It's always been technologically feasible. And they've been dragging their feet for a long time, I think, and for too long - until the pressure simply mounted."