In April 2012, a mere eighteen months after its debut, Instagram was purchased by Facebook for $1 billion. The high-flying start-up's founders had cashed out without ever having devised a business model. No matter: by November the following year, the first ad feed would run in Instagram, following Facebook principles of limited targeting. The acquisition would prove astute. In April 2012 Instagram had 30 million users, but by the fall of 2015 it had 400 million, more than Twitter.

Tim Wu, The Attention Merchants, loc. 1061