How to log off the system using VB.Net?

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

Dim t As Single
Dim objWMIService, objComputer As Object
'Now get some privileges
objWMIService = GetObject("Winmgmts:{impersonationLevel=impersonate,(Debug,Shutdown)}")

For Each objComputer In objWMIService.InstancesOf("Win32_OperatingSystem")
t = objComputer.Win32Shutdown(0, 0)
If t <> 0 Then
MsgBox("Error occurred!!!")
Else
'LogOff your system
End If
Next
End Sub