[TheLastSuperman]

Use/Test at your own risk and don't forget to correct the file paths in the code (based around vB4)

Implementing a CAPTCHA challenge after a certain number of refreshes in vBulletin 4 requires a combination of client-side and server-side scripting. Here's a step-by-step guide to achieve this:

1. Client-Side Scripting:
First, we'll use JavaScript to count the number of page refreshes.

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script type="text/javascript">
var refreshCount = localStorage.getItem('refreshCount') || 0;

$(document).ready(function () {
    refreshCount++;
    localStorage.setItem('refreshCount', refreshCount);

    if (refreshCount > 5) { // Change 5 to the number of refreshes you want to allow before triggering CAPTCHA
        $.ajax({
            url: 'path_to_your_vbulletin/captcha_trigger.php',
            method: 'POST',
            data: { triggerCaptcha: true },
            success: function(response) {
                if (response === 'show_captcha') {
                    // Redirect to a page or pop up a modal to show the CAPTCHA challenge
                    window.location.href = 'path_to_your_vbulletin/show_captcha.php';
                }
            }
        });
    }
});
</script>

2. Server-Side Scripting:
captcha_trigger.php:

This script will handle the AJAX request and set a session variable to trigger the CAPTCHA.

<?php
session_start();

if (isset($_POST['triggerCaptcha']) && $_POST['triggerCaptcha'] == true) {
    $_SESSION['show_captcha'] = true;
    echo 'show_captcha';
}
?>

show_captcha.php:

This script will display the CAPTCHA challenge to the user.

<?php
session_start();

if (isset($_SESSION['show_captcha']) && $_SESSION['show_captcha'] == true) {
    // Display your CAPTCHA challenge here. You can use vBulletin's built-in CAPTCHA or integrate with a third-party service like reCAPTCHA.
    
    // After displaying the CAPTCHA, reset the session variable
    $_SESSION['show_captcha'] = false;
} else {
    // If the session variable is not set, redirect the user back to the main page
    header('Location: path_to_your_vbulletin/main_page.php');
}
?>

3. Integration with vBulletin:

• Add the client-side script to the footer or header template of your vBulletin theme so it runs on every page load.
• Place the server-side scripts (captcha_trigger.php and show_captcha.php) in the root directory of your vBulletin installation or an appropriate sub-directory.
• Ensure that the paths in the AJAX request and redirection match the locations of your server-side scripts.

This solution will present a CAPTCHA challenge to the user after they refresh the page a certain number of times. Adjust the threshold as needed. Remember to test thoroughly before deploying to a live environment, I recommend using a staging environment / cloned or copied version of your main site.