You can check in your template if the current user is logged in:
{def $currentUser=fetch( 'user', 'current_user' )}
{if $currentUser.is_logged_in}
{* here comes the stuff only for users that have logged in *}
...
{/if}
{undef $currentUser}
{let user=fetch( user, current_user )}
{section show=$user.is_logged_in}
{* here comes the stuff only for users that have logged in *}
{/section} {/let}