Caller ID is a signal from the network, not proof of identity. On international routes it can be hidden or replaced.
Why a number can be hidden
- The caller enabled number withholding.
- The call comes through a PBX or call centre that does not pass the number.
- An international gateway stripped the field.
How spoofing works
In SIP telephony the "from" field is filled by the sender. A carrier can validate it or not. That is why a call "from your bank" can originate anywhere while displaying the bank's official number.
What it means
Treat the displayed number as a label, not as an identity. If the caller asks for a code, a password or a transfer, end the call and dial the organisation yourself.
Can you trace the real number
Not on your own. The operator sees the route of the call and can identify the origin on a lawful request. Services that promise to reveal it sell databases or take your money.
Practical protection
- Never authenticate by inbound call.
- Use call blocking for numbers you do not recognise, if your phone supports it.
- Enable two-factor authentication with an app rather than SMS where possible.
See also: checking a number for spam, fake bank SMS.