Quad9 is a public DNS resolver service that enhances user privacy and security while browsing the internet. Founded as a nonprofit organization, it provides a free domain name system (DNS) service that blocks access to known malicious websites, helping to prevent phishing attacks, malware, and other cyber threats. By routing DNS queries through its secure infrastructure, Quad9 ensures that user data is not logged or shared, promoting a more private online experience. The service is designed to be easy to configure and is available for both individual and enterprise use.