Caller ID Display

Caller-ID Spoofing

by Rich Pasco

Caller Identification, or “Caller ID” for short, is a system by which the phone number of a calling party is transmitted in parallel with the ringing signal to a telephone set. With conventional wired and cellular telephone services, the number of the calling party is determined accurately from telephone company records and transmitted by the carrier's equipment. Unfortunately this is not the case with Voice-over-Internet-Protocol (VoIP) telephone systems. With VoIP systems, the callerID number originates from the caller's computer. An honest VoIP caller enters his number correctly into his VoIP software when he sets up VoIP, and it is transmitted to people he calls. But a dishonest VoIP caller can enter any number he wants, even a different one for each call. This process, called “Caller ID Spoofing”, enables junk callers to put any number they want on your Caller ID when your phone rings. In many ways it is analogous to e-mail address spoofing.

They use this capability in five evil ways:

  1. Never the Same Number Twice
  2. Spoofing a Known Institution
  3. Spoofing a Local Number
  4. Spoofing a Loved One
  5. Your Own Number and Voicemail Security

Other sections of interest:

1. Never the Same Number Twice

Scammers, knowing that people tend to block numbers which originate junk calls, often spoof a different, random number on every call they make. There really is no point in blocking such a number, because they'll probably never use it again. And if you're really unlucky, the number they spoof might really belong to someone from whom you might want to receive a call on another occasion, whom you wouldn't want to inadvertently block.

Personally, I only bother block numbers if they (a) leave more than one junk voicemail, and (b) show up as “Scam or Fraud” in the reverse-lookup feature of

One morning my cell phone rang with a number I didn't recognize. When I answered, a recording said “This is cardholder services, calling about your current credit card account....” Since it did not mention which account, I knew it was phony, and so I added the number to my growing list of “do not ring” numbers. But probably they will not use that number again anyway.

2. Spoofing a Known Institution

Pacific Gas & Electric

Pacific Gas & Electric My home land line rang, displaying the number 800-743-5000 (which happens to be the main customer service number for Pacific Gas & Electric). I answered on the first ring, but as I said “hello” the caller hung up. Thinking this odd, I called PG&E back and followed the menu prompts about “suspicious phone calls” to learn that there is an on-going scam where callers spoof PG&E's number and demand payment for an allegedly overdue account. Actually I am glad that my caller hung up, but annoyed that they called at all.

On another day, I received another call also apparently from PG&E. This time when I answered, the caller launched into a spiel about how my account was overdue, and I needed to pay up right now or else my power would be turned off, and he would be happy to take my credit card number over the phone. I asked, “So please tell me, which account number are you calling about?” He immediately rattled off a ten-digit number. I said, “Please excuse me while I verify that against my most recent bill.” I went to fetch the bill, but by the time I had returned with it (bearing an account number not even close to the one he had given me), he had already hung up.

Visa Global Customer Care

Visa Scam Alert On Wednesday, February 28, 2018, while on another call, I was alerted to a call waiting from Visa Global Customer Care at 800-847-2911. I let it roll to voicemail, but no message was left, so I called back, worked my way through the menu tree, and pressed Zero for a representative. I said I was returning their call and asked what that call was about. The representative asked whether I had recently reported a card lost or stolen. When I said “no” she explained that the only time they make outgoing calls is to follow up on such reports, but a scammer has been spoofing their number onto calls offering to lower interest rates, as a way of tricking people into divulging their card numbers and other personal information.

DHL Express ServicePoint

DHL On Friday, June 22, 2018, I received a voicemail for which the caller ID showed DHL Express ServicePoint at (800) 225-5345 (their real number). I think it was spoofed because (1) I was not expecting a package from DHL, and (2) the recording was in Chinese (I think), which I don't speak. If you can understand it, please contact me with a rough translation

According to reports at, the DHL number is frequently spoofed to get past our natural defenses.

Other Agencies

Sometimes a scam caller will claim to represent the FBI, IRS, or some other agency and invite you to Google their number to “prove” it. The result may show that the agency's real number matches that on your caller ID, except that they're not really calling from that number—they only spoofed it!

For more reading

3. Spoofing a Local Number

Scammers often spoof a number whose area code and “prefix”—first six digits total—match the number of the victim they are calling, because they know people are more likely to pick up a call whose origin looks local, assuming that it is a neighbor. In reality, the caller could be anywhere in the world. A good rule of thumb is, if you don't recognize the name that comes with the caller ID, or the calling number is not in your contacts, let it roll to voicemail. If it's important, the caller will leave a message.

Often, in spoofing a local number, a scammer will choose a number which actually belongs to someone in your community. On more than one occasion when I have called back such a local number, the legitimately innocent party there was completely unaware that their number had been spoofed onto spam calls. There is no point in getting angry at such a person (it's not their fault) or in blocking the number (it probably won't be used again), but politely explaining what happened may help them understand other angry calls they may have received. You may want to give them a link to this article.

About that name

Some caller-ID displays (usually on land-lines) display a name alongside the number of the calling party. The way caller ID works, only the number is sent with the call; your local phone company (the one ringing your phone) looks up the associated name to be displayed on your caller ID. So if a scammer calling from the other side of the world spoofs a number in your community, your local phone company will look up and display the name of your neighbor who owns that number, even though the scammer may not know it.

The situation is a little different with some phones (usually cell phones) which instead of displaying a name looked up by the phone company but instead look up the calling number in your personal contact list.

For more information

4. Spoofing a Loved One

In San Jose, California in October 2018, Eric Greenwood received a call, apparently from his wife's cell phone since her name and contact photo appeared. He heard screaming and crying in the background, as a male voice told him that his wife had been kidnapped, and demanded $1500 ransom. After he had paid the ransom, he called back to his wife's phone. She answered and said she was fine and knew nothing of any kidnapping. That was when he realized he'd been scammed.

For more information

5. Your Own Number and Voicemail Security

On Wednesday evening, April 18, 2007, I got a call on my cell phone, apparently from a telemarketer. He gave his name as “David” and said he was calling from the “American Grant Information Center” and that my number was randomly selected by computer from among all US residents and that I was eligible to receive free grant money. [Yeah, sure!]

For this call, my caller-ID indicator displayed as the calling number my own cell phone number! Obviously, I was not calling myself, so his computer was falsifying its caller ID through a technique known as “Caller-ID Spoofing” (see above). When placing a call with the right equipment and software, it is relatively easy to forge any number you wish to be displayed as the caller. In this case “David” was setting a fictitious calling number matching the actual called number (mine). Find more about Caller-ID Spoofing in Google and Wikipedia

Furthermore, he was calling me in violation of the fact that my cell phone number was listed on the National Do Not Call Registry.

I asked “David” for his company's phone number “so that I can call you back” but he refused to divulge it, insisting on sticking to his own patter about free grant money for me. I told him that I was on the Do Not Call registry and that his phone call was illegal unless he fully identified his company and their phone number. Actually, it was illegal regardless, but I wanted as much information as I could get to file with my complaint. He wouldn't tell me any more so I hung up.

Next I visited the National Do Not Call Registry and filed a complaint, giving the name of the company as “American Grant Information Center” with unknown phone number. Not much for them to go on, but better than nothing, I suppose.

But here's the most important part, and it's really scary:

Suppose I had not answered the call? My [former] cell phone service Cingular (now AT&T Wireless) forwarded all calls which are not answered directly into their voicemail system. By default, when that system recognizes the caller ID as matching the phone number whose mailbox is being called, it automatically logs the caller in with the full authority to control the system (play incoming messages, set personal options, record new greetings, etc.). Therefore, if I hadn't answered, “David” would have had full control over my voicemail system!

Closing this exposure was simple: I just needed to configure my voicemail system to always ask for my password regardless of the caller ID. On Cingular's system this is called “Turn off 'Skip Password'” and is implemented by logging into voicemail and pressing these keys:

4 - Options
2 - Administrative options
1 - Password options
2 - “Skip Password” control
2 - Turn “Skip Password” off

If you have a non-Cingular system your exact keys may vary, but the principle is the same.

Now I'm wondering whether “David” really was a telemarketer, or if perhaps his “free grant money” patter was really a cover for his real purpose of looking for unsecured voicemail systems he could hack into, perhaps for purposes of harvesting personal information for nefarious purposes.

The moral of this story is:

If your voicemail system doesn't always ask you for your password, I strongly recommend that you reconfigure it so that it does. Otherwise, a hacker, easily spoofing your own number as their own, could call right in and take over your voicemail system, playing and deleting your messages, changing your settings, and more.

How to Spot a Phony

So if you can't trust the caller ID, how do you know whether a phone call is legitimate or phony?

First off, certain agencies never make outbound phone calls. The Internal Revenue Service and Social Security Administration are examples. So if you get a call ostenisbly from one of these, you know it's phony.

Second, a legitimate caller will ask for you by name. If they immediately launch into a spiel about “your” account without first asking for you by name, then they are phony: they assume that any “you” who answers the phone is fair game. If you fall for it, to paraphrase Carly Simon, You're so vain, you prob'ly think this call is about you, don't you, don't you?

Third, even if they do ask for you by name, ask them to tell you the account number they are calling about. If they rattle off a number, ask them to hold while you match it against your recent statement. If they don't match, don't talk to them. Under no circumstances should you give out your account number to a stranger calling on the phone! Your bank or service provider will already know your account number, so if they ask for it you know they are a scammer trying to extract that information from you.

Finally, if they have your name and account number correctly, thank them politely for the heads up and hang up. Then call the number on the back of your card or on your billing statement to further investigate the issue with your account. Never call back on the number that the stranger calling you gave (unless it happens to be the company's real number).


Note: As author of this page, I see my primary responsibility as warning potential victims of caller-ID spoofing not to believe the caller ID displayed on their phone by an incoming call. It violates my conscience to advertise ways to do it. However, I feel it is only appropriate to fully expose at least one method of caller-ID spoofing simply to illustrate how easy it is. I am surprised that it legal, but apparently it is.

SpoofCard is a commercial subscription service. For a fee, subscribers can place their outgoing calls through the SpoofCard server instead of directly. When placing a call, the subscriber enters the number to be called and the number to appear on the caller ID. It's that simple.



Further Research

General Information about Caller ID

To check numbers which call you

About caller ID spoofing

More about robocalls in general

About voicemail security

About the “American Grant Information Center”

Other Phone Scams

If you have any questions feel free to e-mail me.

Index to all of Rich Pasco's articles on e-mail and viruses

Rich Pasco's home page

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