  Ransomware has remained one of the most notorious threats in the
cybersecurity field. Moving Target Defense (MTD) has been proposed as a novel
paradigm for proactive defense. Although various approaches leverage MTD, few
of them rely on the operating system and, specifically, the file system,
thereby making them dependent on other computing devices. Furthermore, existing
ransomware defense techniques merely replicate or detect attacks, without
preventing them. Thus, this paper introduces the MTFS overlay file system and
the design and implementation of three novel MTD techniques implemented on top
of it. One delaying attackers, one trapping recursive directory traversal, and
another one hiding file types. The effectiveness of the techniques are shown in
two experiments. First, it is shown that the techniques can delay and mitigate
ransomware on real IoT devices. Secondly, in a broader scope, the solution was
confronted with 14 ransomware samples, highlighting that it can save 97% of the
files.
