Short answer
A VPN leak happens when your IP address, DNS queries or other network information is visible even though the VPN is active.
Common types
The most common leaks are DNS leaks, WebRTC leaks and IPv6 leaks. They can let websites or network observers see more than you intended.
Why leaks happen
Leaks can be caused by VPN settings, operating system networking, browser features or a VPN service that does not handle IPv6 properly.
How to reduce the risk
Use a kill switch, enable DNS protection in the VPN app, check IPv6 support and test your IP address after connecting. Keep the VPN client updated.
Common questions
Do all VPN services protect against leaks?
No. Features and default settings vary between providers.
Is a leak always dangerous?
It depends on your threat model, but leaks reduce privacy and should be fixed.