A large multinational enterprise recently integrated a digital HR onboarding system to streamline applicant submissions...

Comprehensive and Detailed Explanation (ECIH-aligned):

This incident demonstrates a document-based web malware delivery mechanism, specifically leveraging remotely hosted Rich Text Format (RTF) injection, which is explicitly discussed in ECIH web and malware handling modules. RTF documents can reference external objects or templates, allowing malicious payloads to be fetched dynamically when the document is opened—without requiring macros or user interaction.

Option A is correct because the behavior described aligns precisely with remote template injection. The absence of macros, the silent external connections, and the use of structural document elements are classic indicators of RTF-based malware delivery. ECIH highlights this as a high-risk technique because it bypasses traditional macro-based detection and user warning mechanisms.

Option B is incorrect because the payload was delivered via downloaded documents, not email impersonation of social contacts. Option C references browser extensions and PDFs, which are not involved. Option D describes lateral spread, not initial delivery.

ECIH emphasizes that modern web-based attacks increasingly abuse trusted document formats and remote object references to evade controls. Understanding these techniques enables responders to improve document sanitization, outbound traffic monitoring, and content disarm and reconstruction (CDR) controls.