They&#x27;re rare that we know of.  If the various intelligence&#x2F;security institutions know how to find&#x2F;train them, surely they wouldn&#x27;t tell everyone as it then destroys their tactical advantage.<p>I&#x27;m not suggesting that I <i>know</i> they&#x27;re common by any stretch of the imagination.  But to say that you <i>know</i> they aren&#x27;t is intellectually dishonest.