TL;DR: There's no symptom to watch for here — the risk is that a phone still holds photos, messages, saved passwords, and app data until it's deliberately and completely erased before resale or disposal. Back up anything you want to keep, sign out of iCloud or your Google account and remove the SIM/SD card, then use Settings > General > Transfer or Reset iPhone > Erase All Content and Settings (iPhone) or Settings > System > Reset options > Erase all data (Android), confirming encryption is enabled beforehand for extra assurance.
There's no symptom to watch for here — the risk is that a phone still holds photos, messages, saved passwords, and app data until it's deliberately and completely erased before resale or disposal.
What Usually Causes This
A basic factory reset can sometimes leave recoverable data behind on devices with certain older storage configurations, and skipping account sign-out first can leave the device locked to the previous owner or leave synced data accessible.
What to Do About It
Back up anything you want to keep, sign out of iCloud or your Google account and remove the SIM/SD card, then use Settings > General > Transfer or Reset iPhone > Erase All Content and Settings (iPhone) or Settings > System > Reset options > Erase all data (Android), confirming encryption is enabled beforehand for extra assurance.
If this looks similar to something else you've seen, it's worth reading How to Spot a Fake Browser Extension.
This pattern shows up elsewhere too — see How to Spot a Fake Public WiFi Hotspot.
Frequently Asked Questions
What are the real warning signs?
There's no symptom to watch for here — the risk is that a phone still holds photos, messages, saved passwords, and app data until it's deliberately and completely erased before resale or disposal.
What usually causes this?
A basic factory reset can sometimes leave recoverable data behind on devices with certain older storage configurations, and skipping account sign-out first can leave the device locked to the previous owner or leave synced data accessible.
What should I do about it?
Back up anything you want to keep, sign out of iCloud or your Google account and remove the SIM/SD card, then use Settings > General > Transfer or Reset iPhone > Erase All Content and Settings (iPhone) or Settings > System > Reset options > Erase all data (Android), confirming encryption is enabled beforehand for extra assurance.
Should I be worried if I only see one sign?
One sign alone (like a slower device) is usually not cause for alarm — most single symptoms have mundane explanations. Multiple signs together, especially unexpected data usage or unfamiliar apps, are worth investigating.