As discussed in \S~\ref{software-and-non-copyright} of this tutorial,

\href{http://www.law.cornell.edu/uscode/text/17/1201}{17 USC~\S1201} and

relate sections\footnote{These sections of the USC are often referred to as

  the ``Digital Millennium Copyright Act'', or ``DMCA'', as that was the name

  of the bill that so-modified these sections of the USC\@.} prohibits users

from circumventing technological measures that implement DRM\@.  Since this

is part of copyright law and the GPL is primarily a copyright license, and

since what the DMCA calls ``circumvention'' is simply ``modifying the

software'' under the GPL, GPLv3 must disclaim such anti-circumvention

provisions are not applicable to the GPLv3'd software.

In the first