由于WordPress 3.4.0，可以将参数过滤到查询中。

add_filter(\'widget_posts_args\', \'wpse_30124\');

function wpse_30124(){
  return array(
    \'posts_per_page\'      => $number,
    \'no_found_rows\'       => true,
    \'post_status\'         => \'publish\',
    \'ignore_sticky_posts\' => true,
    \'cat\' => \'-12\' // term_id of the category you want to exclude
  );
}