1) If your microcontroller has code stored in internal flash memory or eeprom memory, the code could be corrupted by errant re-writing in the code space.

2) As temperature increases so does the probability that a bit in nonvolatile memory will spontaneously change. Under moderate operating temperatures this probability is extremely low. Spontaneous bit changes become likely when the die temperature approaches temperatures that will degrade or destroy it.

3) If you exceed the write endurance of a flash or EEPROM cell the code will be corrupted.

I am sure there are more that I didn't think of/know about. I don't know much about high energy radiation, but that is a concern in RAM's. Maybe it is also a concern in nonvolatile memories.

- Lee