laceous

Due to lack of interest (both my own and based on the number of downloads) this plugin will not be updated for WP 3.0
WordPress’ auth cookies include a built-in expiration date (either 2 or 14 days depending on if the ‘Remember Me’ option is checked). Even if you remove the client-side cookie (by manually logging out or just closing your browser if ‘Remember Me’ wasn’t checked when logging in) the data that was stored within the cookie is still valid until the expiration date is reached.
This could be an issue if someone managed to “steal” your cookie(s). They would still be able to access your website for some time into the future.
This plugin will immediately invalidate your auth cookies when you manually log out. This, of course, also means that you have to manually click ‘Log out’ for this plugin to work properly (you can’t just close your browser to remove any cookies that expire at the end of the session). This won’t prevent session hijacking, but should limit the amount of time that an attacker can access your website.

Invalidate Logged Out Cookies

This plugin will immediately invalidate your auth cookies when you manually log out.

Nate Reist

This plugin simply adds a logout button to the content of any password protected post. Sometimes clients want a password protected page to share information with privileged individuals and the default 10 days for the cookie to expire is too long for their liking. So I wrote a little plugin to do this with AJAX and set the cookie to expire immediately, well actually 10 days in the past.
<ul>
<li>Works logged in or out as a WordPress user.</li>
<li>Uses the same functionality WordPress uses to set post cookies.</li>
<li>Has a simple settings page to make everything easier.</li>
<li>Allows you to alert user they have logged out.</li>
</ul>

Protected Posts Logout Button

Automatically adds a logout button to your password protected content.

Invalidate Logged Out Cookies vs Protected Posts Logout Button