What does the term "phreaking" pertain to?

A.
Spamming mail servers in the hopes of bringing them down

B.
Footprinting and port scanning networks

C.
Fraudulent use of telephone services

D.
Compromising tunneling protocols

Explanation:
A phreaker is a type of hacker that specializes in telephone fraud.
This can be carried out by reconfiguring a telecommunication device, social
engineering, or attacking a companys PBX system.