  Fraud has severely detrimental impacts on the business of social networks and
other online applications. A user can become a fake celebrity by purchasing
"zombie followers" on Twitter. A merchant can boost his reputation through fake
reviews on Amazon. This phenomenon also conspicuously exists on Facebook, Yelp
and TripAdvisor, etc. In all the cases, fraudsters try to manipulate the
platform's ranking mechanism by faking interactions between the fake accounts
they control and the target customers.
