Function to exclude a category(s) from the main loop (pre WP 3.3) in certain categories

gistfile1.aw

add_action( 'pre_get_posts', 'dm_exclude_category_from_category' );

function dm_exclude_category_from_category( $query ) {

global $wp_the_query;
	if( $wp_the_query === $query && $query->is_category( array (4,5,6,7) ) ) {
 		$query->set( 'cat', '-25' );
 	}
}