James is a black hat hacker employed as an authorized officer at Apple. He has credentials and signed a non-disclosure agreement to perform advanced penetration testing on the iOS 6.1.6 operating system, and has already gained low-level access to the mobile device using a backdoor. The process by which John could design/create his own custom firmware to exploit underlying vulnerabilities and gain a higher level of access to a UNIX shell with root privileges, essentially allowing them to do anything on the device is ? a. MMS b. Mobile content management c. RCS d. Jailbreaking.