How Do Apps Prevent Phone Number Spoofing?
Posted: Tue May 27, 2025 8:46 am
Phone number spoofing is a technique where a caller disguises their actual phone number to appear as a different number on the recipient’s caller ID. This can be exploited to impersonate trusted entities, commit fraud, or bypass verification systems. Apps that rely on phone numbers for user verification or communication have developed multiple methods to combat spoofing and ensure the authenticity of phone numbers.
1. Verification via SMS or Call with One-Time Codes
The most common way apps prevent spoofing is by using one-time passcodes (OTP) sent via SMS or automated calls. When you register or log in:
The app sends a unique, time-sensitive code to the phone number entered.
The user must enter this code to verify ownership of the number.
Since only the legitimate owner can receive the SMS or call, spoofing the caller ID alone won’t grant access.
However, this method assumes the attacker does not have control over the actual phone line or the ability to intercept messages.
2. Carrier-Level Authentication: STIR/SHAKEN
To prevent caller ID spoofing at the network level, many recent mobile phone number data telecom carriers have adopted STIR/SHAKEN protocols. These standards:
Authenticate and verify the caller ID information at the source.
Add digital certificates to calls, which receiving carriers can check to confirm the caller ID is legitimate.
Help apps that integrate with carrier data identify calls coming from verified numbers.
While STIR/SHAKEN primarily addresses voice calls, its adoption improves the overall trustworthiness of phone number-based systems.
3. Phone Number Validation Services
Apps often use third-party phone number validation services to:
Check if a number is valid and active.
Determine if the number is a landline, mobile, VoIP, or virtual number.
Detect numbers known for fraud or temporary use.
Validation helps apps flag suspicious numbers that may be used in spoofing attempts or fraudulent registrations.
4. Device and Network Fingerprinting
Advanced apps combine phone number verification with device and network fingerprinting techniques:
Track IP addresses, device IDs, and behavioral patterns during registration.
Detect inconsistencies between the phone number’s registered location and the user’s current IP address or device location.
Spot multiple accounts tied to the same suspicious phone number or device.
These additional data points make spoofing more difficult because attackers must spoof more than just the phone number.
5. Two-Factor and Multi-Factor Authentication
To reduce reliance on phone numbers alone, many apps use two-factor authentication (2FA):
After verifying the phone number, users must provide a second factor, like a password or biometric scan.
This limits damage if a spoofed number is used, as the attacker needs access to additional credentials.
Multi-factor authentication enhances security beyond phone number verification.
6. User Reporting and Machine Learning Detection
Apps encourage users to report suspicious calls or messages, feeding data into machine learning systems that:
Analyze patterns of spoofing attempts.
Automatically flag or block numbers involved in fraudulent activities.
Continuously update filters to detect new spoofing techniques.
Crowdsourced feedback improves app defenses over time.
7. Limitations and Ongoing Challenges
Spoofing techniques evolve rapidly, making it a cat-and-mouse game.
Some sophisticated attackers can intercept SMS or calls using SIM swapping or SS7 network attacks.
VoIP numbers complicate detection, as they are easier to spoof and often shared.
Therefore, while apps use multiple layers of defense, complete prevention is challenging. Combining phone number verification with additional security measures remains the best approach.
Conclusion
Apps prevent phone number spoofing through a multi-layered approach involving SMS/call verification, carrier authentication protocols like STIR/SHAKEN, phone number validation, device fingerprinting, and multi-factor authentication. User reports and AI-driven detection further strengthen defenses. Although spoofing cannot be eliminated entirely, these methods significantly reduce risks and protect both users and services from fraudulent activities.
1. Verification via SMS or Call with One-Time Codes
The most common way apps prevent spoofing is by using one-time passcodes (OTP) sent via SMS or automated calls. When you register or log in:
The app sends a unique, time-sensitive code to the phone number entered.
The user must enter this code to verify ownership of the number.
Since only the legitimate owner can receive the SMS or call, spoofing the caller ID alone won’t grant access.
However, this method assumes the attacker does not have control over the actual phone line or the ability to intercept messages.
2. Carrier-Level Authentication: STIR/SHAKEN
To prevent caller ID spoofing at the network level, many recent mobile phone number data telecom carriers have adopted STIR/SHAKEN protocols. These standards:
Authenticate and verify the caller ID information at the source.
Add digital certificates to calls, which receiving carriers can check to confirm the caller ID is legitimate.
Help apps that integrate with carrier data identify calls coming from verified numbers.
While STIR/SHAKEN primarily addresses voice calls, its adoption improves the overall trustworthiness of phone number-based systems.
3. Phone Number Validation Services
Apps often use third-party phone number validation services to:
Check if a number is valid and active.
Determine if the number is a landline, mobile, VoIP, or virtual number.
Detect numbers known for fraud or temporary use.
Validation helps apps flag suspicious numbers that may be used in spoofing attempts or fraudulent registrations.
4. Device and Network Fingerprinting
Advanced apps combine phone number verification with device and network fingerprinting techniques:
Track IP addresses, device IDs, and behavioral patterns during registration.
Detect inconsistencies between the phone number’s registered location and the user’s current IP address or device location.
Spot multiple accounts tied to the same suspicious phone number or device.
These additional data points make spoofing more difficult because attackers must spoof more than just the phone number.
5. Two-Factor and Multi-Factor Authentication
To reduce reliance on phone numbers alone, many apps use two-factor authentication (2FA):
After verifying the phone number, users must provide a second factor, like a password or biometric scan.
This limits damage if a spoofed number is used, as the attacker needs access to additional credentials.
Multi-factor authentication enhances security beyond phone number verification.
6. User Reporting and Machine Learning Detection
Apps encourage users to report suspicious calls or messages, feeding data into machine learning systems that:
Analyze patterns of spoofing attempts.
Automatically flag or block numbers involved in fraudulent activities.
Continuously update filters to detect new spoofing techniques.
Crowdsourced feedback improves app defenses over time.
7. Limitations and Ongoing Challenges
Spoofing techniques evolve rapidly, making it a cat-and-mouse game.
Some sophisticated attackers can intercept SMS or calls using SIM swapping or SS7 network attacks.
VoIP numbers complicate detection, as they are easier to spoof and often shared.
Therefore, while apps use multiple layers of defense, complete prevention is challenging. Combining phone number verification with additional security measures remains the best approach.
Conclusion
Apps prevent phone number spoofing through a multi-layered approach involving SMS/call verification, carrier authentication protocols like STIR/SHAKEN, phone number validation, device fingerprinting, and multi-factor authentication. User reports and AI-driven detection further strengthen defenses. Although spoofing cannot be eliminated entirely, these methods significantly reduce risks and protect both users and services from fraudulent activities.