Back in the early 2000s, the internet had a problem with child pornography. Tracking these illegal activities became much more difficult, and removing all trace of the images from the World Wide Web seemed nearly impossible. So government officials turned to Silicon Valley for help. But technology companies dragged their feet. By 2008 little had been done to fix the issue of online child pornography until one tech honcho—Microsoft—contacted Dartmouth College computer scientist Hany Farid. Farid is an expert in photo forensics, techniques used most often to identify fake images. Together Farid and Microsoft built a tool to identify any image by a unique signature, like a photo fingerprint. With that signature Microsoft could compare images—before they got posted on websites—to a database of nearly 30,000 images of child pornography catalogued by the National Center for Missing and Exploited Children. Now Farid is ready to use this same technology to fight another internet specter—terrorist messaging. According to the Counter Extremism Project (CEP), online terrorist videos and images play an important role in radicalizing extremists. Silicon Valley is again dragging its feet to find a solution, even as evidence mounts that content hosted on their websites is in part responsible for recent acts of terrorism.