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hotdiggity on 07/08/10

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Last Edited at 07/08/10 11:25am

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Invisible Captcha

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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.

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Copy this code and paste it in your HTML 
  1. HTML:
  2. <div class="hidebox">
  3. Please leave blank: <input type="text" id="gotcha" tabindex="-1" name="gotcha" />
  4. </div>
  5.  
  6. PHP:
  7. <?php
  8. if($_POST["gotcha"]!=""){
  9. header("Location: {$_SERVER[HTTP_REFERER]}");exit;
  10. }
  11. ?>
  12.  
  13. CSS:
  14. .hidebox {
  15.     position:absolute;
  16.     background-color:#CC0000;
  17.     left:0px;
  18.     top:-500px;
  19.     width:1px;
  20.     height:1px;
  21.     overflow:hidden;
  22. }
  23.  
  24. Note for WordPress:
  25. /wp-content/themes/theme-name/comment.php
  26. add around line 65 (after author,email,url inputs):
  27. <!--Catch sp@m-->
  28. <p class="hidefield"><input type="text" name="gotcha" id="gotcha" size="22" tabindex="-1" />
  29. <label for="gotcha"><small><?php _e('Leave blank!'); ?></small></label>
  30. </p>
  31.  
  32. /wp-comments-post.php
  33. Add after approx. line 54:
  34. $comment_gotcha       = ( isset($_POST['gotcha']) ) ? trim($_POST['gotcha']) : null;
  35.  
  36. Add after approx. line 87:
  37. if ( $comment_gotcha != '' ) die( __('Error: Your post has been rejected as spam') );	
  38.  
  39. i.e., after 
  40.  
  41. if ( '' == $comment_content )
  42. 	wp_die( __('Error: please type a comment.') );
  43.  
  44. /wp-content/themes/theme-name/style.css
  45. .hidefield { position:absolute; background-color:#CC0000; left:0px; top:-500px; width:1px; height:1px; overflow:hidden; }

URL: http://www.bensky.co.uk/blog/code-tutorials/invisible-capcha-concept-stop-spam-email/

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