After analyzing and correlating activity from multiple sensors, the security analyst has determined a group from a high-

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After analyzing and correlating activity from multiple sensors, the security analyst has determined a group from a high-risk country is responsible for a sophisticated breach of the company network and continuous administration of targeted attacks for the past three months. Until now, the attacks went unnoticed.
This is an example of:

A. privilege escalation.
B. advanced persistent threat.
C. malicious insider threat.
D. spear phishing.