What are the potential security risks of not deleting sessions or cookies when a user logs out or closes their browser window?

If sessions or cookies are not deleted when a user logs out or closes their browser window, it can lead to potential security risks such as session hijacking or unauthorized access to the user's account. To mitigate these risks, it is important to properly destroy sessions and delete cookies when a user logs out or closes their browser.

// Destroy session and delete cookies when user logs out
session_start();
$_SESSION = array();
session_destroy();

// Delete cookies
setcookie('cookie_name', '', time() - 3600, '/');