The correct answer is A. Call Spoofing because the defining behavior in the scenario is manipulating the caller ID information so that the victim’s phone displays a trusted number—specifically, the credit union’s official line. In CEH-aligned social engineering and mobile attack discussions, call spoofing is a technique where an attacker falsifies caller ID data to impersonate a legitimate organization, department, or known contact. This increases credibility and exploits human trust in recognized numbers, making victims more likely to comply with sensitive requests such as disclosing usernames, passwords, or one-time codes.

The attack is also a form of vishing (voice phishing), where the attacker uses phone calls and persuasive pretexts (“mandatory security check”) to trick employees into revealing credentials. The success factor here is the authority and legitimacy signal created by the spoofed number. When staff see what appears to be an official institutional phone number, they are more likely to assume the call is authentic and bypass normal verification steps, especially under time pressure or when framed as a security requirement.

Why the other options are incorrect: OTP hijacking refers to stealing or intercepting one-time passwords (for example via SIM swap, malware, or social engineering focused specifically on MFA/OTP codes). While the attacker could ask for OTPs, the scenario’s core mechanism is the spoofed caller ID, not OTP interception. Bluebugging is a Bluetooth-based attack that gains unauthorized control over a device through Bluetooth vulnerabilities; it is unrelated to caller ID impersonation. SMiShing is phishing via SMS/text messages, not a voice call.

Therefore, the mobile attack vector demonstrated—displaying a trusted institutional number to deceive employees during a credential-harvesting call—is call spoofing.