License clarification.

LICENSE

@@ -1,3 +1,11 @@
+--- A note on GPL versions
+
+BusyBox is distributed under version 2 of the General Public License (included
+in its entirety, below).  Version 2 is the only version of this license which
+this version of BusyBox (or modified versions derived from this one) may be
+distributed under.
+
+------------------------------------------------------------------------
 		    GNU GENERAL PUBLIC LICENSE
 		       Version 2, June 1991
 

docs/busybox.net/license.html

@@ -1,12 +1,15 @@
 <!--#include file="header.html" -->
 
 <p>
-<h3>BusyBox is licensed under the GNU General Public License</h3>
+<h3>BusyBox is licensed under the GNU General Public License, version 2</h3>
 
 <p>BusyBox is licensed under <a href="http://www.gnu.org/licenses/gpl.html#SEC1">the
-GNU General Public License</a> version 2, which is generally
+GNU General Public License</a> version 2, which is often abbreviated as GPLv2.
-abbreviated as the GPL.  (This is the same license the Linux kernel is under,
+(This is the same license the Linux kernel is under, so you may be somewhat
-so you may be somewhat familiar with it by now.)</p>
+familiar with it by now.)</p>
+
+<p>A complete copy of the license text is included in the file LICENSE in
+the BusyBox source code.</p>
 
 <p><a href="/products.html">Anyone thinking of shipping BusyBox as part of a
 product</a> should be familiar with the licensing terms under which they are
@@ -22,6 +25,42 @@ you violate the license terms, and thus infringe on the copyrights of BusyBox.
 (This requirement applies whether or not you modified BusyBox; either way the
 license terms still apply to you.)  Read the license text for the details.</p>
 
+<h3>A note on GPL versions</h3>
+
+<p>Version 2 of the GPL is the only version of the GPL which current versions
+of BusyBox may be distributed under.  New code added to the tree is licensed
+GPL version 2, and the project's license is GPL version 2.</p>
+
+<p>Older versions of BusyBox (versions 1.2.2 and earlier, up through about svn
+16112) included variants of the recommended "GPL version 2 or (at your option)
+later versions" boilerplate permission grant.  Ancient versions of BusyBox
+(before svn 49) did not specify any version at all, and section 9 of GPLv2
+(the most recent version at the time) says those old versions may be
+redistributed under any version of GPL (including the obsolete V1).  This was
+conceptually similar to a dual license, except that the different licenses were
+different versions of the GPL.</p>
+
+<p>However, BusyBox has apparently always contained chunks of code that were
+licensed under GPL version 2 only.  Examples include applets written by Linus
+Torvalds (util-linux/mkfs_minix.c and util_linux/mkswap.c) which stated they
+"may be redistributed as per the Linux copyright" (which Linus clarified in the
+2.4.0-pre8 release announcement in 2000 was GPLv2 only), and Linux kernel code
+copied into libbb/loop.c (after Linus's announcement).  There are probably
+more, because all we used to check was that the code was GPL, not which
+version.  (Before the GPLv3 draft proceedings in 2006, it was a purely
+theoretical issue that didn't come up much.)</p>
+
+<p>To summarize: every version of BusyBox may be distributed under the terms of
+GPL version 2.  New versions (after 1.2.2) may <b>only</b> be distributed under
+GPLv2, not under other versions of the GPL.  Older versions of BusyBox might
+(or might not) be distributable under other versions of the GPL.  If you
+want to use a GPL version other than 2, you should start with one of the old
+versions such as release 1.2.2 or SVN 16112, and do your own homework to
+identify and remove any code that can't be licensed under the GPL version you
+want to use.  New development is all GPLv2.</p>
+
+<h3>License enforcement</h3>
+
 <p>BusyBox's copyrights are enforced by the <a
 href="http://www.softwarefreedom.org">Software Freedom Law Center</a>, which
 "accepts primary responsibility for enforcement of US copyrights on the