An IP address can reveal a lot about you. It is a unique number assigned to all devices connected to the Internet. Both your IPv4 and IPv6 addresses are used to identify your location and device uniquely. That is exactly what a VPN should prevent, so it is important to check that your real addresses are not routed past the VPN.
Domain Name Service (DNS) translates the domain name of a website into IP addresses. This is necessary to establish a connection to the server on which a web page or service is hosted. A DNS leak means you are using your providers' DNS server and are not using the VPN tunnel. With this test, you can ensure that your DNS requests are anonymous and encrypted over the VPN.
The WebRTC API definition allows browsers to perform audio and video chats and P2P file sharing without installing a plugin. WebRTC has a mechanism to find out the publicly accessible IP. If there is a WebRTC leak in your system, you will see two public IP addresses: The one assigned by the VPN server and the one assigned by your internet provider. Try it now!
A security problem in Windows systems means that attackers can access your Windows login data. This would also give them access to other Microsoft services that you use. If your system is vulnerable to this, the MSLeak test will show you your Windows username and possibly the password or at least the password hash. If this is the case, please change your password immediately after the MSLeak test!