Yeah they are, that said, the guys that do this tend to hit easy targets. They know which cars are a breeze. These little boost bullets tuck their convertor up high and tight close to the engine. It takes a good while to actually pull one out to change it. Cutting the upper end of our cats would be extremely difficult. That by no means assures they aren't a target but there are a 30 models that are an easier hit than an Explorer ST.
EDIT: TMAC types faster than I do.