John, a professional hacker, performs a network attack on a renowned organization and gains unauthorized access to the t

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John, a professional hacker, performs a network attack on a renowned organization and gains unauthorized access to the target network. He remains in the network without being detected for a long time and obtains sensitive information without sabotaging the organization.
Which of the following attack techniques is used by John?

A. Insider threat
B. Diversion theft
C. Spear-phishing sites
D. Advanced persistent threat