What Is Caller ID Spoofing and Shielding? (STIR/SHAKEN)
Caller ID spoofing occurs when a call displays a number that misrepresents its origin or the caller’s identity. Caller ID shielding usually means blocking your number from appearing to the person you call; it does not authenticate you or make a call anonymous. STIR/SHAKEN lets phone providers sign and check claims about calling numbers, but it cannot prove a caller’s intent or prevent every spoof.
People often use “caller ID shielding” to mean keeping their own number private. Others use it to describe a phone company’s warning or blocking tools for incoming calls. Those are different functions, and neither is the same as STIR/SHAKEN.
The key distinction is simple: privacy controls limit what a recipient sees, while call authentication helps providers check whether a calling-number claim has been vouched for. Neither one tells you whether a call is safe to answer. Below is how to tell these systems apart and what to do when a call looks suspicious.
Distinguish spoofing, caller-ID blocking, and authentication
Spoofing, blocking, and authentication solve separate problems. Spoofing concerns a possibly false number display. Blocking is a privacy request that may hide your number from the recipient. STIR/SHAKEN is a provider-to-provider system for checking a signed claim about a calling number.
Caller ID spoofing means a displayed number misrepresents the call’s originating number or caller identity. A caller may use a number that belongs to someone else, or choose a number that resembles a local one. The display alone does not reveal who placed the call.
Not every call that displays a number different from the caller’s direct line is unlawful. A business may use an authorized main number for outbound calls. Under 47 U.S.C. § 227(e) and 47 CFR § 64.1604, knowingly transmitting misleading or inaccurate caller-ID information is prohibited when done with intent to defraud, cause harm, or wrongfully obtain something of value. The circumstances and intent matter.
Caller-ID blocking asks a carrier not to show your number to the person you call. In the United States, *67 may request per-call blocking where the carrier and call type support it. A persistent blocking option may also be available through your provider. Blocking does not encrypt a call, prove that you are legitimate, or hide your number from the carriers handling it.
STIR/SHAKEN is a system that lets voice providers sign and verify information about a call’s claimed calling number. STIR defines the Internet-protocol signing approach; SHAKEN describes how U.S. providers use it. The system supports authentication of a number claim, not verification of a person’s identity or reason for calling.
| Feature | Main purpose | What it does not establish |
|---|---|---|
| Caller-ID blocking, such as *67 | Requests that your number not appear to the recipient | Anonymity, encryption, or legitimacy |
| Caller-ID spoofing | Alters or misrepresents the displayed number | Who actually placed the call |
| STIR/SHAKEN | Lets providers sign and verify call-identity information | Caller intent, honesty, or safety |
Key takeaway: A blocked number is not automatically spoofed, and a verified number is not a guarantee that a call is safe.
What caller-ID shielding does—and does not—hide
“Caller-ID shielding” is not one precise technical or legal term. In everyday use, it usually means blocking your number on outgoing calls, or masking a business caller’s direct number with an authorized public number. Ask your carrier or phone service what feature is being offered and what information it hides.
When you use a supported blocking feature, the recipient may see a label such as “Private” or “Unknown” instead of your number. The exact result depends on the carrier, phone system, and type of call. Some destinations, including certain toll-free or emergency services, may handle caller-ID information differently. Check your provider’s terms rather than assuming *67 works on every call.
Blocking is a display preference, not a way to defeat STIR/SHAKEN. It does not stop the network from handling call information needed to route the call, and it does not make a caller untraceable. Nor does it prevent a recipient from declining blocked calls.
Number masking in a business phone service is different from simple blocking. For example, a company may present its published customer-service number when staff call from separate lines. That can be a legitimate use when the organization is authorized to use the number. It should not be confused with permission to impersonate another person or organization.
Keep these limits in mind:
- A number hidden from the person you call may still be available to carriers involved in the call.
- Blocking your number does not authenticate you or stop unwanted calls.
- A call marked “verified” can still be a sales call, a scam, or otherwise unwanted.
- An unverified call is not necessarily fraudulent; the network may lack the information needed to check it.
Next step: If privacy is your goal, ask your originating carrier about per-call and persistent blocking, how emergency and toll-free calls are handled, and whether recipients can reject blocked calls.
How providers sign, verify, and handle calls
STIR/SHAKEN operates between voice providers, not as a personal identity check displayed directly to every caller. In an IP-based call, the originating provider can sign call-identity information in a SIP Identity header using a PASSporT token. A receiving provider can check that signature and use the result in its own call-handling decisions.
The main technical references include RFC 8224 for SIP identity handling, RFC 8225 for PASSporT, and ATIS-1000074 for the SHAKEN framework. U.S. provider requirements appear in 47 CFR §§ 64.6300–64.6305. These rules govern provider practices; they do not promise that every call will receive a visible verification label.
In broad terms, the process works like this:
- The originating provider determines what it can verify about the customer and the calling number.
- Where required and technically supported, it signs the call-identity information.
- A downstream provider checks the signature and associated information.
- The receiving provider may use its result, along with other signals and its policies, to label, allow, or block the call.
A call can pass through older networks or gateways that do not carry the relevant information end to end. A signature can also fail verification. These outcomes do not, by themselves, prove fraud. Providers may apply separate analytics and blocking rules, so the label or handling can differ between phone services.
What A, B, and C attestation mean
Attestation describes what the originating provider says it knows about the call. It is not a rating of the caller’s character, and it does not prove the call’s purpose is benign.
- A, or full attestation: The provider authenticated its customer and verified that the customer is authorized to use the calling number.
- B, or partial attestation: The provider authenticated its customer but did not verify that the customer is authorized to use the number.
- C, or gateway attestation: The provider is handling the call as a gateway and cannot authenticate the originating customer.
An A-level attestation is stronger evidence about the provider’s knowledge of the number claim than B or C. It still does not certify that the caller is who they say they are in conversation, or that the request they make is trustworthy.
Check suspicious calls and report suspected spoofing
A careful record helps you separate a privacy issue from a suspicious number claim. I would first note what appeared on the phone, then check the call with the provider rather than treating a label or number as proof. Keep the evidence factual and avoid calling back a number supplied by a suspicious caller.
Record these details:
- The displayed number and any “Private,” “Spam,” or verification label.
- The date and time, including your time zone.
- Your receiving carrier and the device or phone service used.
- What the caller claimed, especially requests for money, passwords, or one-time codes.
- Whether the call was expected and whether the caller left a message.
Then contact your carrier through a known official channel. Ask whether call details or authentication results are available and how to submit a fraud report. If you suspect illegal caller-ID spoofing, you can also report it to the FCC. Provide the facts you recorded; do not assume that an unfamiliar or failed verification result proves a crime.
Practical call scenarios
These examples are illustrative, not reports of specific investigations. They show how the same display can have different explanations.
| Situation | What it may mean | Sensible response |
|---|---|---|
| A family member’s number appears, but they deny calling | Possible spoofing, account issue, or another explanation | Contact them using a saved number; report repeated incidents to your carrier |
| Your call displays “Private” after using *67 | Caller-ID blocking may be working | Ask your carrier about limits if the recipient cannot accept blocked calls |
| An incoming call shows a verified label but requests a payment code | The provider checked a number claim; the request remains untrusted | Hang up and contact the organization using a number you independently know |
| A legitimate business call has no verification label | The call may have crossed a network that did not provide usable verification information | Verify the caller through the business’s official contact channel |
A useful rule is to verify high-impact requests outside the call. If someone claims to represent a bank, utility, government office, or family member and asks for money or sensitive information, end the call and contact that party using a trusted number. Caller-ID data can help with screening, but it should not be the only test.
Conclusion: use privacy and authentication for what they do
Caller-ID blocking limits what the recipient may see; STIR/SHAKEN lets providers check a signed claim about a calling number. Neither offers anonymity, proves a caller’s identity, nor guarantees safety. Use carrier privacy settings for display control, and use independent verification for suspicious requests. Report suspected spoofing to your provider and the FCC with the call details you recorded.
Frequently asked questions
Is caller-ID spoofing illegal?
It is prohibited under federal law when someone knowingly transmits misleading or inaccurate caller-ID information with intent to defraud, cause harm, or wrongfully obtain something of value. The facts and intent matter.
Does *67 stop STIR/SHAKEN?
No. *67 requests caller-ID blocking where supported. It does not defeat STIR/SHAKEN, erase network records, or make the call anonymous.
Does STIR/SHAKEN prove who is calling?
No. It helps providers authenticate information about the calling number. It does not prove a person’s identity, honesty, or purpose.
What does an A attestation mean?
It means the originating provider authenticated its customer and verified that the customer is authorized to use the calling number. It is not a guarantee that the call is safe.
What do B and C attestation mean?
B means the provider authenticated its customer but did not verify authority to use the number. C means it handled the call as a gateway and could not authenticate the originating customer.
Can a legitimate call be unverified?
Yes. A call may lack usable verification information because of its provider, network path, or a gateway. An unverified result alone does not show that the call is fraudulent.
Can a verified call still be a scam?
Yes. Verification concerns the provider’s assertion about the number, not the caller’s intent. Treat requests for money, passwords, or codes with care, even when a label appears.
How do I report suspected caller-ID spoofing?
Record the number, time, label, and details of the call. Follow your carrier’s fraud-reporting process and submit a report to the FCC if you suspect illegal spoofing.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
