What is 9.9.9.9?
9.9.9.9 is the primary DNS resolver address of Quad9, a non-profit public DNS service. Quad9 blocks domains known to be used for malware, phishing, and other threats using threat intelligence from IBM X-Force and other partners. It does not log personally identifiable information and is headquartered in Zurich, Switzerland.
Privacy note
If 9.9.9.9 appears in a DNS leak test, your system or network is configured to use Quad9. This is generally considered a privacy-respecting choice, but if you're on a VPN and see this address, check whether your VPN is enforcing its own DNS resolver.