Since 2008, the National Center for Missing & Exploited Children (NCMEC) has offered to share with ISPs a list of hash values that correspond to known child abuse images. That list, which was eventually coupled with Microsoft’s own PhotoDNA technology, has enabled companies like Google, Microsoft, ISPs and others to check large volumes of files for matches without those companies themselves having to keep copies of offending images, and without human eyes having to invade users’ privacy by scanning their email accounts for known child abuse images. Earlier this month, the Counter Extremism Project (CEP) unveiled a software tool that works in a similar fashion and urged the big internet companies to adopt it.