get unique machine id

You can use WMI Code creator. I guess you can have a combination of "keys" (processorid,mac and software generated key).

using System.Management;
using System.Windows.Forms;

try
{
     ManagementObjectSearcher searcher = 
         new ManagementObjectSearcher("root\\CIMV2", "SELECT * FROM Win32_Processor"); 

     foreach (ManagementObject queryObj in searcher.Get())
     {
         Console.WriteLine("-----------------------------------");
         Console.WriteLine("Win32_Processor instance");
         Console.WriteLine("-----------------------------------");
         Console.WriteLine("Architecture: {0}", queryObj["Architecture"]);
         Console.WriteLine("Caption: {0}", queryObj["Caption"]);
         Console.WriteLine("Family: {0}", queryObj["Family"]);
         Console.WriteLine("ProcessorId: {0}", queryObj["ProcessorId"]);
     }
}
catch (ManagementException e)
{
    MessageBox.Show("An error occurred while querying for WMI data: " + e.Message);
}

Win32_Processor

Retrieving Hardware Identifiers in C# with WMI by Peter Bromberg