Random posts loop

i have used the loop for my theme homepage
but when i go page 2 or 3 , 4 …etc
i got the same random posts in all pages i wanna make the loop generate different random posts each page .

<?php query_posts("showposts=8&orderby=rand"); ?>
              <?php if ( have_posts() ) : while ( have_posts() ) :                     the_post(); ?>
<-- quotes content -->
              <?php endwhile; else: ?>
              <p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
              <?php endif; ?>