The Kill Switch and DNS Leak Protection are security features available for the ZenMate VPN Desktop Client for Windows. The features can be enabled and disabled in the settings menu in the client.
The Kill Switch feature prevents data leaks by making sure your device only has internet access if the connection is going through the VPN. Because of this, no data will be processed on the device if the VPN for some reason loses connection.
DNS Leak Protection
DNS, or Dynamic Name System, is used to translate a domain name into an IP address. A DNS server works a bit like a phone book and knows what IP address goes with what domain name.
When you want to open a website, the DNS server looks up what IP address you are "calling", connects you to the server where that IP is hosted, and opens the right site in your browser. When you are not using a VPN, your ISP uses its own DNS servers to find the website you are looking for.
When using ZenMate, all this is instead done within the VPN tunnel and your ISP cannot see what page you are visiting.
Unfortunately, it sometimes happens that Windows goes its own way and uses the default settings. This means that the request is sent via the ISP rather than through ZenMate and the ISP can see what page is visited. This is known as a DNS leak.
The DNS Leak Protection feature prevents this from happening by making sure that the DNS request cannot be performed by the native platform but only by ZenMate.