Because you never know if the person over the phone is trying to scam you or not, so if you were to give them your ssn they would use your identity for stuff that they want. I hope this helps :)
Answer:
b. the IP address can be spoofed, so if you want to read response from the deceived party, you can use IP spoofing to hide yourself.
Explanation:
The answer to your question is b crowding out effect
