Answer from cs61c-aq (Anjali Jagannatha Koppal 16454392) for Question 1
When converting instructions to machine code, commands and values are all converted to just ones and zeroes.
By just switching off one bit, someone could totally change the meaning of the entire code, without it being noticeable or rectifiable for a long time. One technique that could prevent this is strong documentation of code and lots of back-up, but this would include waste of memory and time.