Manage this tool at: Menu ▸ Settings ▸ Active Protection ▸ Secure DNS
SecureDNS protects you against DNS (Domain Name System) hijacking. Some malicious programs can quietly redirect you from an authentic URL to an inauthentic website to acquire sensitive information such as usernames, passwords, and credit card details that you enter.
Every time you enter the URL of a web site such as www.avast.com in your browser, the URL is converted to the IP address of the web server where the target web page is stored. SecureDNS provides an encrypted connection between your web browser and Avast's own DNS server to be sure the translation is not hijacked. In other words, SecureDNS ensures that the displayed web page is the authentic one.
This feature can be enabled or disabled with the blue slider switch in Settings ▸ Active protection.