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Revision: 28450
at April 2, 2012 14:06 by hotdiggity
Updated Code 
HTML:
<div class="hidebox">
Please leave blank: <input type="text" id="gotcha" tabindex="-1" name="gotcha" />
</div>

PHP:
<?php
if($_POST["gotcha"]!=""){
header("Location: {$_SERVER[HTTP_REFERER]}");exit;
}
?>

CSS:
.hidebox {
    position:absolute;
    background-color:#CC0000;
    left:0px;
    top:-500px;
    width:1px;
    height:1px;
    overflow:hidden;
}

Note for WordPress:
/wp-content/themes/theme-name/comment.php
add around line 65 (after author,email,url inputs):
<!--Catch sp@m-->
<p class="hidefield"><input type="text" name="gotcha" id="gotcha" size="22" tabindex="-1" />
<label for="gotcha"><small><?php _e('Leave blank!'); ?></small></label>
</p>

/wp-comments-post.php
Add after approx. line 54:
$comment_gotcha       = ( isset($_POST['gotcha']) ) ? trim($_POST['gotcha']) : null;

Add after approx. line 87:
if ( $comment_gotcha != '' ) die( __('Error: Your post has been rejected as spam') );	

i.e., after 

if ( '' == $comment_content )
	wp_die( __('Error: please type a comment.') );

/wp-content/themes/theme-name/style.css
.hidefield { position:absolute; background-color:#CC0000; left:0px; top:-500px; width:1px; height:1px; overflow:hidden; }

Revision: 28449
at July 8, 2010 11:29 by hotdiggity
Updated Code 
HTML:
<div class="hidebox">
Please leave blank: <input type="text" id="gotcha" tabindex="-1" name="gotcha" />
</div>

PHP:
<?php
if($_POST["gotcha"]!=""){
header("Location: {$_SERVER[HTTP_REFERER]}");exit;
}
?>

CSS:
.hidebox {
    position:absolute;
    background-color:#CC0000;
    left:0px;
    top:-500px;
    width:1px;
    height:1px;
    overflow:hidden;
}

Revision: 28448
at July 8, 2010 11:25 by hotdiggity
Initial Code 
HTML:
<div class="hidebox">
Please leave blank: <input type="text" id="gotcha" tabindex="-1" name="gotcha" />
</div>

PHP:
<?php
if($_POST["gotcha"]!=""){
header("Location: {$_SERVER[HTTP_REFERER]}");exit;
}
?>

CSS:
input#gotcha {
    position:absolute;
    background-color:#CC0000;
    left:0px;
    top:-500px;
    width:1px;
    height:1px;
    overflow:hidden;
}
Initial URL 
http://www.bensky.co.uk/blog/code-tutorials/invisible-capcha-concept-stop-spam-email/
Initial Description 
Create a textbox that the bot will presume is just a field it can exploit with rubbish and label it with an indicator to let any viewers without the privileges of CSS know that it is to be left blank.
Initial Title 
Invisible Captcha
Initial Tags 

                                

                                                            

                                    

                                        

                                        Initial Language
                                        

                                    

                                    
PHP