  This paper studies the physical consequences of a class of unobservable
state-and-topology cyber-physical attacks in which both state and topology data
for a sub-network of the network are changed by an attacker to mask a physical
attack. The problem is formulated as a two-stage optimization problem which
aims to cause overload in a line of the network with limited attack resources.
It is shown that unobservable state-and-topology cyber-physical attacks as
studied in this paper can make the system operation more vulnerable to line
outages and failures.
