[Mko]

I normally have two pretty effective methods to stop spammers.
#1. reCAPTCHA. Go to http://www.google.com/recaptcha and register to get a Public and Private key. Then, in a new tab/window, open up your Forum's Admin Control Panel and go to vBulletin Options -> Human Verification Manager.
Select the 'reCAPTCHA' button and hit save. After doing so, the page will refresh, and you'll see the reCAPTCHA options. Paste the corresponding public/private keys into the fields then select the color of the reCAPTCHA. Then, you're all done.

ONLY DO THIS STEP IF YOUR FORUM USES HTTPS:
However, if you use https:// for your Forums, you'll need to do some template editing. Under the Human Verification Template group, you'll see the template called 'humanverify_recaptcha'.
Replace the contents of it (shown below):

<fieldset class="fieldset">
    <legend>$vbphrase[image_verification]</legend>
    <input id="hash" type="hidden" name="${var_prefix}[hash]" value="$humanverify[hash]" />
    <script type="text/javascript">
        var RecaptchaOptions = {
            theme : '$humanverify[theme]'
            <if condition="$humanverify['langcode']">,lang : '$humanverify[langcode]'</if>
        };
    </script>
    <div dir="ltr">
    <if condition="$show['recaptcha_ssl']">
        <script type="text/javascript" src="https://api-secure.recaptcha.net/challenge?k=$humanverify[publickey]">
    <else />
        <script type="text/javascript" src="http://api.recaptcha.net/challenge?k=$humanverify[publickey]">
    </if>
    </script>
    </div>

    <noscript>
        <if condition="$show['recaptcha_ssl']">
            <iframe src="https://api-secure.recaptcha.net/noscript?k=$humanverify[publickey]" height="300" width="400" frameborder="0"></iframe>
        <else />
            <iframe src="http://api.recaptcha.net/noscript?k=$humanverify[publickey]" height="300" width="400" frameborder="0"></iframe>
      </if>
       <br />
       <textarea name="recaptcha_challenge_field" rows="3" cols="40">
       </textarea>
       <input type="hidden" name="recaptcha_response_field" value="manual_challenge" />
    </noscript>
</fieldset>

with:

<fieldset class="fieldset">
    <legend>$vbphrase[image_verification]</legend>
    <input id="hash" type="hidden" name="${var_prefix}[hash]" value="$humanverify[hash]" />
    <script type="text/javascript">
        var RecaptchaOptions = {
            theme : '$humanverify[theme]'
            <if condition="$humanverify['langcode']">,lang : '$humanverify[langcode]'</if>
        };
    </script>
    <div dir="ltr">
    <if condition="$show['recaptcha_ssl']">
        <script type="text/javascript" src="https://www.google.com/recaptcha/api/challenge?k=$humanverify[publickey]">
    <else />
        <script type="text/javascript" src="http://api.recaptcha.net/challenge?k=$humanverify[publickey]">
    </if>
    </script>
    </div>

    <noscript>
        <if condition="$show['recaptcha_ssl']">
            <iframe src="https://www.google.com/recaptcha/api/noscript?k=$humanverify[publickey]" height="300" width="400" frameborder="0"></iframe>
        <else />
            <iframe src="http://api.recaptcha.net/noscript?k=$humanverify[publickey]" height="300" width="400" frameborder="0"></iframe>
      </if>
       <br />
       <textarea name="recaptcha_challenge_field" rows="3" cols="40">
       </textarea>
       <input type="hidden" name="recaptcha_response_field" value="manual_challenge" />
    </noscript>
</fieldset>

#2. An extra registration question effectively stops most bots.
I followed THIS GUIDE (which is very clear and useful) on how to implement an extra registration question.


Regards,
Mark