Here is how you can secure the application when using the KeyCheck API. First, you can use a third party .NET obfuscation tool together with the KeyCheck API. This can help to obfuscate or encrypt the assembly against tools like net reflector. Second, the KeyCheck API provides the Key-Value challenge/response authentication to protect against DLL emulation. You can see the code examples under the 'Secure' folder:

Examples\KeyCheck.NET\CSharp_WPF\Secure

Examples\KeyCheck.NET\VB.NET_WPF\Secure