Prevent comment bot spamming in WordPress.

<?php
/******* in functions.php of active theme ********/

/**
* Proposition of Use of tellyworth suggestion to avoid bot spamming without modifying core
* http://core.trac.wordpress.org/attachment/ticket/10975/wp-comment-nonce-refresh.patch
*/

add_action('pre_comment_on_post', 'amauri_check_hidden_field');

function amauri_check_hidden_field() {
    $user = wp_get_current_user();
    if ( !isset($_POST['_wpnonce']) || !wp_verify_nonce($_POST['_wpnonce'], "comment_form_{$comment_post_ID}") ) {
        do_action('comment_nonce_failed', $comment_post_ID);
        wp_die( __('Sorry, automated comments are not accepted.') );
    }
}

add_action('comment_form', 'amauri_add_hidden_field');

function amauri_add_hidden_field() {
    wp_nonce_field("comment_form_{$post_id}", '_wpnonce', false);
}