Understanding Caller ID Spoofing

Photo by Lindsey LaMont on Unsplash

What is Caller ID?

When you get a phone call, your phone displays the number of the person who is calling you, this is caller ID. A name can also be displayed, but the name technically is not part of the caller ID system. Call names are provided by another system called CNAM.

How does Caller ID Work?

When a call is made, your phone sends the number it has configured. Your service provider receives that number and is responsible to validate (or not) the number. They also can look up the caller’s subscriber name to have it displayed.

It used to be that your service provider would keep track of all the numbers that were tied to the Central Office switch. But that was the old days when we only had Plain Old Telephone Service (POTS) lines. With today’s market of hundreds of local/long distant carriers, there is no central authority or regulation on caller ID. The FCC does not regulate the carrier’s accuracy of their caller ID databases.

What is Caller ID Spoofing?

Caller ID spoofing is when someone changes the number that your phone shows when you receive a call. With today’s technology, it is relatively easy for anyone to change the number that is displayed. Caller ID is not verified, so don’t take it as 100% accurate.

By changing their caller ID number, they can:

  1. Hide their real phone number
  2. Make you believe a trusted person is calling (Bank, Doctor, Store)

Neighbor Spoofing

One of the techniques used is called Neighbor Spoofing. This is when the caller ID is changed to a phone number similar to your number. This is to make you think someone local area is calling you. If you think someone you know (neighbor/friend) is calling, then you are more likely to answer the call. Still do not answer, if it is important they will leave a message or call back.

How is it Spoofed?

It used to be somewhat difficult to change the caller ID number. There were hardware devices like the Orange Box, that emulated the Bell 202 FSK signal. And you had to know what you were doing.

But today it is much simpler with Voice over IP. Digital signals can easily be altered to change the caller ID. You don’t even need to understand how to do it, there are even services that will do it for you. SpoofTel and Spoof My Phone are just a few of many services that allow you to change your caller ID.

Is Caller ID Spoofing Illegal?

Technically, caller ID spoofing is not illegal in all cases. It becomes illegal when the number is changed with the intent to defraud, cause harm or obtain private information. Legitimate reasons to use caller ID spoofing is for businesses that want to display the main office number, rather than showing the specific desk number. Or perhaps employees that don’t work at the office (sales) and use their personal phones.

How to Prevent being Tricked?

Because fraudsters can change the caller ID number to any number, you may not always be able to tell that the number calling you is spoofed. A common indicator is when the caller tries to ask you for personal information and/or money. No legitimate business is going to be calling you asking for money. If you get a call like that and you believe it could be true, then hand up and call the business directly. Look up their phone number (don’t use any number that the phone caller may have given you.) and call them.


  • Don’t answer calls from unknown numbers
  • Never give out information freely. Like answering the phone with “Hello, this is John”
  • If you believe it’s really someone from a company or service you use, have them verify your account details (account number or last bill amount) before talking with them.

The FCC has some good tips as well, see them here.

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