  We initiate the analysis of the response of computer owners to various offers
of defence systems
  against a cyber-hacker (for instance, a botnet attack), as a stochastic game
of a large number of interacting agents. We introduce a simple mean-field game
that models their behavior. It takes into account both the random process of
the propagation of the infection (controlled by the botner herder) and the
decision making process of customers. Its stationary version turns out to be
exactly solvable (but not at all trivial) under an additional natural
assumption that the execution time of the decisions of the customers (say,
switch on or out the defence system) is much faster that the infection rates.
