A security analyst for a large financial institution is creating a threat model for a specific threat actor that is like

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A security analyst for a large financial institution is creating a threat model for a specific threat actor that is likely targeting an organization's financial assets.
Which of the following is the BEST example of the level of sophistication this threat actor is using?

A. Social media accounts attributed to the threat actor
B. Custom malware attributed to the threat actor from prior attacks Most Voted
C. Email addresses and phone numbers tied to the threat actor
D. Network assets used in previous attacks attributed to the threat actor
E. IP addresses used by the threat actor for command and control