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In a word:
The program/automaton("the weird machine") somehow eventually gets to an unexpected state by itself through at least one unexpected state transformation, which is caused by a user-crafted data flow.
It's from a pure technical viewpoint and has nothing to do with some so-called branches/categories of "security"(such as OpSec, Reverse Engineering, Forensics(without exploitation), Unauthorized access, or something like that).
The point here is whether there's any *unexpected* and exploitable behavior involved in the target *itself*.
Just my humble opinion, feel free to correct me.