client can \textit{only} exercise this control over its own copyrighted

changes to the GPL-covered program.  The parts of the program it obtained

from other contributors must be provided to the contractor with the usual GPL

freedoms.  Thus, GPLv3 permits users to convey covered works to contractors

operating exclusively on the users' behalf, under the users' direction and

control, and to require the contractors to keep the users' copyrighted

changes confidential, but \textit{only if} the contractor is limited to acting

on the users' behalf (just as the users' employees would have to act).

The strict conditions in this ``contractors provision'' are needed so that it

cannot be twisted to fit other activities, such as making a program available

to downstream users or customers.  By making the limits on this provision

full freedoms of the GPL that they deserve.

The FSF was specifically asked to add this ``contractors provisions'' by

large enterprise users of Free Software, who often contract with non-employee

developers, working offsite, to make modifications intended for the user's

private or internal use, and often arrange with other companies to operate

their data centers.  Whether GPLv2 permits these activities is not clear and

may depend on variations in copyright law in different jurisdictions.  The

practices seem basically harmless, so FSF decided to make it clear they are

permitted.

GPLv3~\S2's final paragraph includes an explicit prohibition of sublicensing.

\section{GPLv3~\S3: What Hath DMCA Wrought}

\label{GPLv3s3}

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

provisions are not applicable to the GPLv3'd software.  GPLv3\S3 shields

users from being subjected to liability under anti-circumvention law for

exercising their rights under the GPL, so far as the GPL can do so.

First, GPLv3\S3\P1 declares that no GPL'd program is part of an effective

technological protection measure, regardless of what the program does.  Early

drafts of GPLv3\S3\P1 referred directly to the DMCA, but the final version

instead includes instead an international legal reference to

anticircumvention laws enacted pursuant to the 1996 WIPO treaty and any

similar laws.  Lawyers outside the USA worried that a USA statutory reference

could be read as indicating a choice for application of USA law to the

license as a whole.  While the FSF did not necessarily agree with that view,