Logout from a website e.g. facebook

Hi,

I need to make a script for autologin. I fund it over internet :

# Edit this to be the URL or IP address of the site to launch on login
 
$Url = “www.microsoft.com”
 
# Edit this to be the username
 
$Username=”name@microsoft.com”
 
# Edit this to the corresponding password
 
$Password=”password”
 
# Edit this to be the path to the executable.  Include the executable file name as well.
 
$Executable = "c:\windows\system32\notepad.exe"
 
# Invoke Internet Explorer
 
$IE = New-Object -com internetexplorer.application;
$IE.visible = $true;
$IE.navigate($url);
 
# Wait a few seconds and then launch the executable.
 
while ($IE.Busy -eq $true)
 
{
 
Start-Sleep -Milliseconds 2000;
 
}
 
# The following UsernameElement, PasswordElement, and LoginElement need to be modified first.  See the notes at the top
# of the script for more details.
 
$IE.Document.getElementById(“UsernameElement”).value = $Username
$IE.Document.getElementByID(“PasswordElement”).value=$Password
$IE.Document.getElementById(“SubmitElement”).Click()
 
while ($IE.Busy -eq $true)
 
{
 
Start-Sleep -Milliseconds 2000;
 
}
 
Invoke-Item $Executable




It is working but problem is that, if session is already active for a site it gives error. So for that we need to logout first from that particular site ,and than execute this script. How to write logout script for a website in which session is already active.