Blocking access to taxonomy pages
while category/year/2525 is an alias for taxonomy/term/xxx you should restrict access to taxonomy/term/* for all anonymous users.

if you want do this via simple module:

function mymodule_init(){
  global $user;
  if(arg(0) == 'taxonomy' &amp;&amp; arg(1) == 'term' &amp;&amp; !$user-&gt;uid) {
     drupal_access_denied();
     exit;
  }
}