I thought I'd share some links I've found to check for DNS leaks:
If you see your real IP or another IP (other than the one that you are connected to by VPN) then you have a DNS leak.
You should fix it by setting static IP and DNS server settings on your network adapter.
I've written a step-by-step guide for people unfamiliar with network and IP settings.
Instructions on how to make your IP settings static for Windows 7:
You might be asked to elevate system priviledges or authenticate as Admin while you perform these steps, just allow it all.
Click on the network icon on the taskbar (the lower right screen near the clock) -> Click on "Network and sharing center" -> Click on "Change adapter settings" on the menu to the left.
You need to know your router's network settings before you continue: Right click on your network adapter (Local area connection if you're connected by a LAN cable or Wireless network connection if WiFi) and choose "Status" -> Click on "Details...". There you should notice your "IPv4 Address", "IPv4 Subnet Mask", "IPv4 Default Gateway" and "IPv4 DNS Server". Click "Close" and again "Close".
Right click on your network adapter and choose "Properties" -> Click on "Internet Protocol Version 4" (don't un-check it) and click "Properties".
Select the "Use the following IP address" button.
IP address: When you noticed your "IPv4 Address" in the "Details" screen earler, it might have looked like this: 192.168.0.1 or 192.168.1.1. This was an IP address assigned by the DHCP pool on your router and happens automatically. You might think to put in the same IP address as you saw in the "Details" window but if you do that, the IP address might be assigned to another computer while your computer is turned off. You should choose an IP address that's much higher than your current IP address so it will be unlikely that another computer will get the same IP address from the DHCP pool.
When you put in the "IP address" on the "Properties" screen, you should put in the same first three numbers (e.g. 192.168.0.) and then the last number should be a random number between 100 and 250. It doesn't really matter what number you choose, you are just choosing a number that should be unused on your local LAN. If you get an error about an "IP address conflict", you should choose another last number in the IP address.
Subnet mask: Copy the "IPv4 Subnet Mask" from earlier.
Default gateway: Copy the "IPv4 Default Gateway" from earlier. This is the IP address of your router.
Preferred DNS server: Put in "10.4.0.1". This is AirVPN's DNS server.
Alternate DNS server: Put in "10.5.0.1". AirVPN's DNS server.
What you have done here is tell Windows to only use AirVPN's DNS servers instead of your routers (or ISP's) DNS servers. If you are not connected to an AirVPN server, you cannot go to the internet unless you put in your normal DNS server settings that you should have noticed in the "Details" screen before (IPv4 DNS Server above).
You can also put AirVPN's website IP address in your "Hosts" file. This means that you can get to Airvpn.org to download a config without constantly changing your DNS server settings. Here's how you do it:
Open notepad.exe as Admin (Right click -> Run as Administrator). Go to File -> Open. You need to navigate to this folder: "C:\Windows\System32\drivers\etc" and it might involve changing folder settings ("Organize" -> "Folder and search options") to show hidden files (View -> Show hidden files). The folder might appear to be empty but change the document type from "Text Document" to "All files" and then open the file called "hosts".
Put in this lines at the bottom:
Then save the file as "hosts" and overwrite the old one. If you didn't run notepad.exe as Admin then you can't save the file.
Hopefully this guide will help people. If there are any questions, just ask!