This scenario describes steganographic sniffing, a highly sophisticated technique covered in CEH v13 Network Sniffing and Steganography. By embedding sensitive data inside legitimate image files—such as CT scans—attackers can intercept or exfiltrate patient information while avoiding detection.

Option D represents a steganography-based covert channel, which is extremely difficult to identify because:

The file appears legitimate

Standard encryption and IDS tools do not flag it

Medical images naturally contain large data volumes

Options A and B involve malware, which is more detectable. Option C involves text-based covert channels, which are easier to analyze than binary image embedding.

CEH v13 identifies steganography as one of the hardest data-hiding techniques to detect, making Option D correct.