Public Shared Function GetDirectoryEntry() As DirectoryEntry
        'Of course change the information for the LDAP to your network
        Dim dirEntry As New DirectoryEntry("LDAP://CN=Users,DC=firma,DC=com")
 
        'Setting username & password to Nothing forces
        'the connection to use your logon credentials
        dirEntry.Username = Nothing
        dirEntry.Password = Nothing
        'Always use a secure connection
        dirEntry.AuthenticationType = AuthenticationTypes.Anonymous
        Return dirEntry
    End Function
 
    Public Function IsValidADLogin(ByVal givenName As String, ByVal surName As _
      String) As Boolean
        Try
            'Create a DirectorySearcher Object (used for searching the AD)
            Dim search As New DirectorySearcher(GetDirectoryEntry)
 
            'Set the filter on the searcher object to look for the 
            ' SAMAccountName, givenName
            ' and the sn (Sur Name)
            'search.Filter = String.Format("((givenName={0})(sn={1}))", 
            ' givenName, surName)
            search.Filter = String.Empty
 
            'Now load these properties to the search
            search.PropertiesToLoad.Add("cn")
 
            'Use the .FindOne() Method to stop as soon as a match is found
            Dim result As SearchResult = search.FindOne()
            'Now check to see if a result was found
            If result Is Nothing Then
                'Login isn't valid
                Return False
            Else
                'Valid login
                Return True
            End If
        Catch ex As Exception
            MessageBox.Show(ex.Message, "Active Directory Error", _
              MessageBoxButtons.OK, MessageBoxIcon.Error, _
              MessageBoxDefaultButton.Button1)
        End Try
    End Function