VB.net Validating that the same computer is accessing a database

Hi

I use the code below to get the following items

 GetProcessorId, MACAddress, VolumeSerial, MotherBoardID

When a user runs my software for the first time I store these four items and then
each time the user tries to access my system I validate that these items are the same.
The MACAddress is causing problems as it returns multiple values.
Which of the other three items will most reliably return the same values every time?

Imports System
Imports System.Management
Imports System.Windows.Forms


Public Class clsComputerInfo

    Public Function GetProcessorId() As String
        Dim strProcessorId As String = String.Empty
        Dim query As New SelectQuery("Win32_processor")
        Dim search As New ManagementObjectSearcher(query)
        Dim info As ManagementObject

        For Each info In search.Get()
            strProcessorId = info("processorId").ToString()
        Next
        Return strProcessorId

    End Function

    Friend Function GetMACAddress() As String

        Dim mc As ManagementClass = New ManagementClass("Win32_NetworkAdapterConfiguration")
        Dim moc As ManagementObjectCollection = mc.GetInstances()
        Dim MACAddress As String = String.Empty
        For Each mo As ManagementObject In moc

            If (MACAddress.Equals(String.Empty)) Then
                If CBool(mo("IPEnabled")) Then MACAddress = mo("MacAddress").ToString()

                mo.Dispose()
            End If
            MACAddress = MACAddress.Replace(":", String.Empty)

        Next
        Return MACAddress
    End Function

    Friend Function GetVolumeSerial(Optional ByVal strDriveLetter As String = "C") As String

        Dim disk As ManagementObject = New ManagementObject(String.Format("win32_logicaldisk.deviceid=""{0}:""", strDriveLetter))
        disk.Get()
        Return disk("VolumeSerialNumber").ToString()
    End Function

    Friend Function GetMotherBoardID() As String

        Dim strMotherBoardID As String = String.Empty
        Dim query As New SelectQuery("Win32_BaseBoard")
        Dim search As New ManagementObjectSearcher(query)
        Dim info As ManagementObject
        For Each info In search.Get()

            strMotherBoardID = info("SerialNumber").ToString()

        Next
        Return strMotherBoardID

    End Function
End Class