Final answer:
The underlined word 'betrays' in the excerpt is a verb that describes the program's action of deceiving and harming the user.
Step-by-step explanation:
The underlined word 'betrays' in the excerpt from The Code Book is a verb. Verbs are words that express actions, occurrences, or states of being. In this case, 'betrays' describes the action that the program designed by Eve performs, which is to deceive and harm the user.
Learn more about part of speech