Lawyers from Facebook, Google and Twitter faced tough questions from Congress about how foreign actors used their platforms to influence the 2016 election. Facebook now says around 130 million Americans were exposed to content created by alleged Russian operatives. Now, all three companies say they plan to try to stop this from happening again. The question is, what can they really do? For some answers, we're joined by Hany Farid. He chairs the computer science department at Dartmouth. Professor Farid created software that is used by tech companies to find and remove bad content like child pornography. And he says his technology could be modified for some of these newer problems.