BROOKE: This is On the Media, I’m Brooke Gladstone.

BOB: And I’m Bob Garfield. Earlier this month, a delegation of top US government officials, including FBI director James Comey and Secretary of Homeland Security Jeh Johnson, met with executives of Apple, Twitter, Facebook, and other tech companies to discuss battling terrorism -- online. One idea was an algorithm that could crawl social sites for signs of radicalization, and assign people a risk value -- like a credit score. The government would then, in theory, use that information to monitor the riskiest subjects. But is that legal? Karen Greenberg is director of the Center on National Security at Fordham University School of Law. Karen, welcome to On the Media.