"Almost seven weeks after a terrorist attack on a New Zealand mosque was streamed live on Facebook, copies of the video are still circulating on Facebook and Instagram. The existence of the videos, some of which have been on the platforms since the day of the attack, are indicative of the challenge tech companies face in combating the spread of white supremacist and other terror-related content on their platforms and raises questions about the effectiveness of Facebook's efforts to do so in particular. 'The problem is that their hashing technology doesn't work the way it is supposed to,' Hany Farid, a professor at Dartmouth and expert in digital forensics and image analysis, told CNN Business, saying it should be able to catch videos that are manipulated. 'When Facebook tells you that artificial intelligence is going to save them and us, you should ask how that is if they can't even deal with the issue of removing previously identified content,' he said."