  The wide adoption of Internet of Things (IoT)-enabled energy devices improves
the quality of life, but simultaneously, it enlarges the attack surface of the
power grid system. The adversary can gain illegitimate control of a large
number of these devices and use them as a means to compromise the physical grid
operation, a mechanism known as the IoT botnet attack. This paper aims to
improve the resiliency of cyber-physical power grids to such attacks.
Specifically, we use an epidemic model to understand the dynamic botnet
formation, which facilitates the assessment of the cyber layer vulnerability of
the grid. The attacker aims to exploit this vulnerability to enable a
successful physical compromise, while the system operator's goal is to ensure a
normal operation of the grid by mitigating cyber risks. We develop a
cross-layer game-theoretic framework for strategic decision-making to enhance
cyber-physical grid resiliency. The cyber-layer game guides the system operator
on how to defend against the botnet attacker as the first layer of defense,
while the dynamic game strategy at the physical layer further counteracts the
adversarial behavior in real time for improved physical resilience. A number of
case studies on the IEEE-39 bus system are used to corroborate the devised
approach.
