  Large-scale load-altering attacks (LAAs) are known to severely disrupt power
grid operations by manipulating several internet-of-things (IoT)-enabled load
devices. In this work, we analyze power grid cascading failures induced by such
attacks. The inherent security features in power grids such as the $N-1$ design
philosophy dictate LAAs that can trigger cascading failures are \emph{rare}
events. We overcome the challenge of efficiently sampling critical LAAs
scenarios for a wide range of attack parameters by using the so-called
``skipping sampler'' algorithm. We conduct extensive simulations using a
three-area IEEE-39 bus system and provide several novel insights into the
composition of cascades due to LAAs. Our results highlight the particular risks
to modern power systems posed by strategically designed coordinated LAAs that
exploit their structural and real-time operating characteristics.
