title: Validity of a GPL exception
body: <p>I have been contracted to modifying software released under the GPL.  The small research company that I am consulting for will be submitting analysis of the output of the modified software as part of a response to a RFP by the US Department of Defense. But there's a catch.</p>
  
  <p>The source directory contains a file called "COPYRIGHT" (along with your standard GPL.txt) that contains the follow text:</p>
  
  <p>"This program is free software.  Permission is hereby granted to use,
  redistribute and/or modify it under the terms of the GNU General Public License
  (GPL) as published by the Free Software Foundation <strong>with the sole EXCEPTION that
  the software and all parts of it may NEVER BE USED FOR ANY MILITARY PURPOSE,
  whether it be research or not, commercial or otherwise.</strong>  You may apply either
  version 2 of the GPL, or (at your option) any later version."</p>
  
  <p>This restriction is clearly incompatible with of section 6 of the GPL (<em>...You may not impose any further restrictions on the recipients' exercise of the rights granted herein...</em>)</p>
  
  <p>So, it appears they have violated the GPL.  </p>
  
  <p>Can I consider their restriction of my GPL rights void?</p>