- Attackers can monitor phones silently using only the victim’s phone number.
- Polling significantly increases battery drain during continuous operation of delivery receipts
- Continuous tracking consumes mobile data and interferes with heavy applications
Security researchers have unveiled a tracking technique called “Silent Whisper” that exploits the way popular messaging apps handle receipts.
The method targets WhatsApp and Signal by abusing low-level message receipts that are automatically exchanged every time an app processes incoming network traffic.
By knowing only a phone number, an attacker can repeatedly probe a device without sending visible messages or triggering notifications.
Impact on battery life and data usage
Silent Whisper runs under the UI, making detection unlikely during normal phone use.
Tests on several smartphones showed unusually high battery consumption during survey activity.
Under normal conditions, idle phones typically lose less than 1% battery per hour.
In testing, an iPhone 13 Pro lost 14% per hour, an iPhone 11 lost 18% per hour, and a Samsung Galaxy S23 lost 15% per hour.
Applying the same approach to Signal only resulted in a 1% battery loss per hour due to stricter rate limiting.
Continuous polls also consume mobile data and disrupt bandwidth-intensive applications such as video calls.
The tracking method is based on measuring round-trip times for delivery receipts.
These response times vary depending on whether a phone is active, inactive, offline, connected to WiFi, or using mobile data.
Steady, fast responses may suggest that a device is actively used in the home, while slower or inconsistent timings may indicate movement or weaker connectivity.
Over extended periods of time, these patterns can reveal daily routines, sleep schedules, and travel behaviors without accessing message content or contact lists.
Although academic research has previously described the vulnerability, a publicly available proof-of-concept tool has now demonstrated its practicality.
The tool allows probes at intervals as short as 50 ms, allowing detailed observation without alerting the target.
The developer warns against misuse and emphasizes search intent, but the software remains accessible to everyone.
This raises concerns about widespread abuse, especially since the vulnerability remains exploitable in December 2025.
Disabling read receipts reduces the exposure of standard messages but does not completely block this technique.
WhatsApp offers an option to block large messages from unknown accounts, although the platform does not set enforcement thresholds.
Signal provides additional controls, but researchers confirmed that probing remains possible.
Traditional antivirus software does not detect misuse at the protocol level.
Services marketed for identity theft protection or malware removal provide limited value when no malware is installed on the device.
This risk is less about data theft and more about persistent behavioral monitoring that users cannot easily observe or verify.
Via Cybernews
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