A multinational corporation's computer system was infiltrated by an advanced persistent threat (APT). During forensic analysis, it was discovered that the malware was utilizing a blend of two highly s

Polymorphic malware changes its code while retaining the original algorithm, often by encrypting parts of itself with different keys, but it doesn't typically rewrite its entire code or use a mutation engine like metamorphic malware.

Macro malware relies on macros within documents (e.g., Office files) to execute, which does not match the description of embedding into system binaries or changing code propagation.

Macro malware is incorrect as it does not typically embed into system files in the manner described, nor does it inherently change its code as it propagates in a metamorphic fashion.

The description of "embedding its harmful code into the actual binary or executable part of genuine system files" strongly indicates a rootkit, which aims to gain persistent and stealthy control by hiding its presence within the operating system. The characteristic of "changes its code as it propagates, making signature-based detection approaches nearly impossible" directly defines metamorphic malware, which rewrites its own code for each infection, often using a "mutation engine," to create functionally identical but syntactically different variants.