  As the number and the diversity of news outlets on the Web grow, so does the
opportunity for "alternative" sources of information to emerge. Using large
social networks like Twitter and Facebook, misleading, false, or agenda-driven
information can quickly and seamlessly spread online, deceiving people or
influencing their opinions. Also, the increased engagement of tightly knit
communities, such as Reddit and 4chan, further compounds the problem, as their
users initiate and propagate alternative information, not only within their own
communities, but also to different ones as well as various social media. In
fact, these platforms have become an important piece of the modern information
ecosystem, which, thus far, has not been studied as a whole.
  In this paper, we begin to fill this gap by studying mainstream and
alternative news shared on Twitter, Reddit, and 4chan. By analyzing millions of
posts around several axes, we measure how mainstream and alternative news flows
between these platforms. Our results indicate that alt-right communities within
4chan and Reddit can have a surprising level of influence on Twitter, providing
evidence that "fringe" communities often succeed in spreading alternative news
to mainstream social networks and the greater Web.
