TL;DR: The simplest check is comparing your IP address and location before and after connecting — sites like whatismyipaddress.com should show a different IP and location once the VPN is active; a DNS leak test confirms your DNS requests are also routed through the VPN. Run an IP-address check and a dedicated DNS leak test both with the VPN on, enable the VPN app's built-in kill switch if it has one so traffic stops entirely if the connection drops, and make sure IPv6 is disabled or properly routed through the VPN if your provider doesn't fully support it.
The simplest check is comparing your IP address and location before and after connecting — sites like whatismyipaddress.com should show a different IP and location once the VPN is active; a DNS leak test confirms your DNS requests are also routed through the VPN.
What Usually Causes This
A VPN can appear "connected" in its app while still leaking your real IP or DNS requests due to misconfiguration, an app bug, or the operating system routing certain traffic outside the VPN tunnel (a known issue called a DNS or IPv6 leak).
What to Do About It
Run an IP-address check and a dedicated DNS leak test both with the VPN on, enable the VPN app's built-in kill switch if it has one so traffic stops entirely if the connection drops, and make sure IPv6 is disabled or properly routed through the VPN if your provider doesn't fully support it.
If this looks similar to something else you've seen, it's worth reading How to Check If Your Router Was Hacked (DNS Hijacking).
This pattern shows up elsewhere too — see How to Remove Spyware From an Android Phone.
Frequently Asked Questions
What are the real warning signs?
The simplest check is comparing your IP address and location before and after connecting — sites like whatismyipaddress.com should show a different IP and location once the VPN is active; a DNS leak test confirms your DNS requests are also routed through the VPN.
What usually causes this?
A VPN can appear "connected" in its app while still leaking your real IP or DNS requests due to misconfiguration, an app bug, or the operating system routing certain traffic outside the VPN tunnel (a known issue called a DNS or IPv6 leak).
What should I do about it?
Run an IP-address check and a dedicated DNS leak test both with the VPN on, enable the VPN app's built-in kill switch if it has one so traffic stops entirely if the connection drops, and make sure IPv6 is disabled or properly routed through the VPN if your provider doesn't fully support it.
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.