I have a login form with user ID and password. After the user logs out, if he then clicks the "Back" button on the browser he might eventally return to the login page and be presented with a message from the browser saying:

"Warning: Page has Expired The page you requested was created using information you submitted in a form. This page is no longer available. As a security precaution, Internet Explorer does not automatically resubmit your information for you.
To resubmit your information and view this Web page, click the Refresh button."

If the user clicks the refresh button and then the retry button of the dialog box, the User ID and password of the login form are resubmitted and the user gains access to the application....

How can I prevent this from happening?

Thanks