Caller ID Spoofing is a technique that displays a phone number different from the actual caller on the recipient's device. In VoIP's SIP protocol, the From header indicating the caller number can be freely configured, making this technically straightforward. While there are legitimate uses such as displaying a company's main number when employees call from personal mobiles, its abuse in bank transfer fraud and vishing is a recurring problem.
Fraud abuse patterns are sophisticated. Spoofing a bank's customer center number to say "There has been unauthorized access to your account" and extracting PINs and one-time passwords. Spoofing a police number to threaten "Your account is being used for criminal activity" and directing transfers to designated accounts. Spoofing a tax office number to claim "You have a tax refund" and guiding ATM operations. In all cases, because the number shown on caller ID appears correct, victims believe they are receiving a legitimate call from an official institution.
Detecting spoofing on the receiving end is difficult. The spoofed number is displayed as-is on the recipient's device, indistinguishable from the real number. The most reliable defense is to never decide anything on the strength of the call alone: hang up and call back using an official contact number you looked up yourself. Banks and government agencies will never ask for PINs or passwords over the phone, so any such request can be immediately identified as fraud.
One technical framework for verifying that a caller number is genuine is STIR/SHAKEN. Carriers attach a digital signature to the caller number, and the receiving carrier checks that signature to judge whether the displayed number was properly assigned to the originating side. Whether the outcome of that check ever reaches your own handset depends on how your carrier handles it, so the practical safeguard on an incoming call is unchanged: do not treat the displayed number as proof, look up the official contact yourself, and call back. Caller ID Spoofing - How It Works and How to Spot It walks through how to check a call you suspect of being spoofed.