FILE - In this March 25, 2015 file photo, Mark Zuckerberg talks about the Messenger app during the Facebook F8 Developer Conference in San Francisco. For the first time, a billion people used Facebook in a single day on Monday, Aug. 24, 2015. Zuckerberg marked the occasion with a post on his Facebook page, saying that one out of seven people on Earth logged in to the social network to connect with their friends and family. (ANSA/AP Photo/Eric Risberg)