  Billions of people rely on essential utility and manufacturing
infrastructures such as water treatment plants, energy management, and food
production. Our dependence on reliable infrastructures makes them valuable
targets for cyberattacks. One of the prime targets for adversaries attacking
physical infrastructures are Programmable Logic Controllers (PLCs) because they
connect the cyber and physical worlds. In this study, we conduct the first
comprehensive systematization of knowledge that explores the security of PLCs:
We present an in-depth analysis of PLC attacks and defenses and discover trends
in the security of PLCs from the last 17 years of research. We introduce a
novel threat taxonomy for PLCs and Industrial Control Systems (ICS). Finally,
we identify and point out research gaps that, if left ignored, could lead to
new catastrophic attacks against critical infrastructures.
