  For reducing threat propagation within an inter-connected network, it is
essential to distribute the defense investment optimally. Most electric power
utilities are resource constrained, yet how to account for costs while
designing threat reduction techniques is not well understood. Hence, in this
work, a vulnerability propagation and a defense model is proposed based on an
epidemic model. The new defense mechanism is then validated through sensitivity
of the propagation parameters on the optimal investment with two-node and
N-node cases. Further, the model efficacy is evaluated with implementation in
one of the communication networks of a cyber-physical power system. Topological
impact on the optimal nodal investment is also emphasized. Optimal investment
of the neighbors with less degree were found to be highly sensitive to
fluctuation in vulnerability exploitability probability.
