  Qualitative evidence suggests that heresy within the medieval Catholic Church
had many of the characteristics of a scale-free network. From the perspective
of the Church, heresy can be seen as a virus. The virus persisted for long
periods of time, breaking out again even when the Church believed it to have
been eradicated. A principal mechanism of heresy was through a small number of
individuals with very large numbers of social contacts.
  Initial attempts by the Inquisition to suppress the virus by general
persecution, or even mass slaughtering, of populations thought to harbour the
"disease" failed. Gradually, however, the Inquisition learned about the nature
of the social networks by which heresy both spread and persisted. Eventually, a
policy of targeting key individuals was implemented, which proved to be much
more successful.
