How to remove URL field from WordPress comments form

Quick tutorial here to help those who are being spammed on their blog.

To remove the URL field from the WordPress comments form simply open functions.php (found within your theme’s directory) in your favourite text editor and paste the following code to it, immediately before the very last line.

add_filter('comment_form_default_fields', 'url_filtered');
function url_filtered($fields)
  return $fields;

Save the file, upload it, and the URL field will have disappeared!