  In recent years, ransomware has been one of the most notorious malware
targeting end users, governments, and business organizations. It has become a
very profitable business for cybercriminals with revenues of millions of
dollars, and a very serious threat to organizations with financial loss of
billions of dollars. Numerous studies were proposed to address the ransomware
threat, including surveys that cover certain aspects of ransomware research.
However, no study exists in the literature that gives the complete picture on
ransomware and ransomware defense research with respect to the diversity of
targeted platforms. Since ransomware is already prevalent in
PCs/workstations/desktops/laptops, is becoming more prevalent in mobile
devices, and has already hit IoT/CPS recently, and will likely grow further in
the IoT/CPS domain very soon, understanding ransomware and analyzing defense
mechanisms with respect to target platforms is becoming more imperative. In
order to fill this gap and motivate further research, in this paper, we present
a comprehensive survey on ransomware and ransomware defense research with
respect to PCs/workstations, mobile devices, and IoT/CPS platforms.
Specifically, covering 137 studies over the period of 1990-2020, we give a
detailed overview of ransomware evolution, comprehensively analyze the key
building blocks of ransomware, present a taxonomy of notable ransomware
families, and provide an extensive overview of ransomware defense research
(i.e., analysis, detection, and recovery) with respect to platforms of
PCs/workstations, mobile devices, and IoT/CPS. Moreover, we derive an extensive
list of open issues for future ransomware research. We believe this survey will
motivate further research by giving a complete picture on state-of-the-art
ransomware research.
