When using a service for your anonymity and privacy, it is extremely important that the traffic coming from your computer is routed through the anonymous network. By any chance leaks of the underlying connection, makes it very easy for any traffic monitor to be able to record all your activities.
DNS or domain name system is used to translate domain names such as www.privacyinternational.org into numeric IP addresses e.g. 126.96.36.199 required to launch data packets on the Internet. Whenever your computer needs to communicate with an Internet server, such as when you enter a URL into your browser, your computer first contacts a DNS server and asks for the IP address. Most ISPs assign their customers a DNS server that they control and use to record your Internet activity.
Under certain circumstances, even when you are connected through an anonymous network, the operating system will continue to use the default DNS servers instead of the anonymous DNS servers.
The leaks DNS is a significant threat to privacy and anonymous networks can provide a false sense of security, when in fact your data is leaked.
If you are concerned about DNS leaks, you can use the website below to find out if they exist.