需求：机器码可以用于校验用户是否用的同一台电脑登录，比如在别的机器上登录时做强制下线（踢人下线）。通常在用户注册时，计算一次用户的机器码跟随注册信息一起发送给服务器。

机器码的作用看百度百科：

定义规则：
机器码 = CPU序列号 + 硬盘ID + 网卡硬件地址

public class MachineCode
{

    static MachineCode machineCode;

    public static string GetMachineCodeString()
    {
        string machineCodeString = string.Empty;
        if (machineCode == null)
        {
            machineCode = new MachineCode();
        }
        machineCodeString = "PC." + machineCode.GetCpuInfo() + "." +
                            machineCode.GetHDid() + "." +
                            machineCode.GetMoAddress();
        return machineCodeString;
    }

    ///   <summary> 
    ///   获取cpu序列号     
    ///   </summary> 
    ///   <returns> string </returns> 
    public string GetCpuInfo()
    {
        string cpuInfo = "";
        try
        {
            using (ManagementClass cimobject = new ManagementClass("Win32_Processor"))
            {
                ManagementObjectCollection moc = cimobject.GetInstances();

                foreach (ManagementObject mo in moc)
                {
                    cpuInfo = mo.Properties["ProcessorId"].Value.ToString();
                    mo.Dispose();
                }
            }
        }
        catch (Exception)
        {
            throw;
        }
        return cpuInfo.ToString();
    }

    ///   <summary> 
    ///   获取硬盘ID     
    ///   </summary> 
    ///   <returns> string </returns> 
    public string GetHDid()
    {
        string HDid = "";
        try
        {
            using (ManagementClass cimobject1 = new ManagementClass("Win32_DiskDrive"))
            {
                ManagementObjectCollection moc1 = cimobject1.GetInstances();
                foreach (ManagementObject mo in moc1)
                {
                    HDid = (string)mo.Properties["Model"].Value;
                    mo.Dispose();
                }
            }
        }
        catch (Exception)
        {

            throw;
        }
        return HDid.ToString();
    }

    ///   <summary> 
    ///   获取网卡硬件地址 
    ///   </summary> 
    ///   <returns> string </returns> 
    public string GetMoAddress()
    {
        string MoAddress = "";
        try
        {
            using (ManagementClass mc = new ManagementClass("Win32_NetworkAdapterConfiguration"))
            {
                ManagementObjectCollection moc2 = mc.GetInstances();
                foreach (ManagementObject mo in moc2)
                {
                    if ((bool)mo["IPEnabled"] == true)
                        MoAddress = mo["MacAddress"].ToString();
                    mo.Dispose();
                }
            }
        }
        catch (Exception)
        {
            throw;
        }
        return MoAddress.ToString();
    }
}

原文地址：

http://group.cnblogs.com/topic/32913.html