TL;DR: If you've never changed your router's admin login from the sticker on the back, that default username/password combination is itself the warning sign, since it's publicly listed for your router's model. Log into the admin panel and change the default admin username and password to something unique, disable remote/WAN-side management if you don't use it, and keep the router's firmware updated to patch known vulnerabilities.
If you've never changed your router's admin login from the sticker on the back, that default username/password combination is itself the warning sign, since it's publicly listed for your router's model.
What Usually Causes This
Router admin panels ship with default, publicly known credentials, and many people never change them, leaving the panel and its settings (including WiFi passwords and DNS) exposed to anyone on the network or, if remote management is on, the internet.
What to Do About It
Log into the admin panel and change the default admin username and password to something unique, disable remote/WAN-side management if you don't use it, and keep the router's firmware updated to patch known vulnerabilities.
If this looks similar to something else you've seen, it's worth reading Signs of Stalkerware on Your Phone.
This pattern shows up elsewhere too — see How to Check If Your Smart Home Devices Are Secure.
Frequently Asked Questions
What are the real warning signs?
If you've never changed your router's admin login from the sticker on the back, that default username/password combination is itself the warning sign, since it's publicly listed for your router's model.
What usually causes this?
Router admin panels ship with default, publicly known credentials, and many people never change them, leaving the panel and its settings (including WiFi passwords and DNS) exposed to anyone on the network or, if remote management is on, the internet.
What should I do about it?
Log into the admin panel and change the default admin username and password to something unique, disable remote/WAN-side management if you don't use it, and keep the router's firmware updated to patch known vulnerabilities.
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.