  Massive amounts of fake news and conspiratorial content have spread over
social media before and after the 2016 US Presidential Elections despite
intense fact-checking efforts. How do the spread of misinformation and
fact-checking compete? What are the structural and dynamic characteristics of
the core of the misinformation diffusion network, and who are its main
purveyors? How to reduce the overall amount of misinformation? To explore these
questions we built Hoaxy, an open platform that enables large-scale, systematic
studies of how misinformation and fact-checking spread and compete on Twitter.
Hoaxy filters public tweets that include links to unverified claims or
fact-checking articles. We perform k-core decomposition on a diffusion network
obtained from two million retweets produced by several hundred thousand
accounts over the six months before the election. As we move from the periphery
to the core of the network, fact-checking nearly disappears, while social bots
proliferate. The number of users in the main core reaches equilibrium around
the time of the election, with limited churn and increasingly dense
connections. We conclude by quantifying how effectively the network can be
disrupted by penalizing the most central nodes. These findings provide a first
look at the anatomy of a massive online misinformation diffusion network.
