\subsection{Right to Private Modification} 

\label{gplv2-private-modification}

The issue of private modifications of GPLv2'd works deserves special

attention.  While these rights are clearly explicit in GPLv3~\S2\P2 (see

\~S\ref{GPLv3S2} of this tutorial for details), the permission to create

private modifications is mostly implicit in GPLv2.  Most notably, the

requirements of GPLv2~\S2 (and GPLv2~\S3, which will be discussed next) are

centered around two different copyright controls: both modification

\emph{and} distribution.  As such, GPLv2~\S2's requirements need only be met

when a modified version is distributed; one need not follow them for modified

versions that are not distributed\footnote{As a matter of best practice, it's

  useful to assume that all software may eventually be distributed later,

  even if there no plans for distribution at this time.  Too often, GPL

  violations occur because of a late distribution decision of software that

  was otherwise never intended for distribution.}.

However, the careful reader of GPLv2 will notice that, unlike GPLv3, no other

clauses of the license actually give explicit permission to make private

modifications.  Since modification of software is a control governed by

copyright, a modifier needs permission from the copyright holder to engage in

that activity.

In practice, however, traditional GPLv2 interpretation has always assumed

that blanket permission to create non-distributed modified versions was

available, and the

\href{http://www.gnu.org/licenses/gpl-faq.html#GPLRequireSourcePostedPublic}{FSF

  has long opined that distribution of modified versions is never mandatory}.

This issue is one of many where GPLv3 clarifies in explicit text the implicit

policy and intent that was solidified via long-standing interpretation of

GPLv2.

the GPLv3 states them herein more explicitly.  In other words, there is no

direct analog to the first sentence of GPLv3~\S2\P2 in GPLv2

(See \S~\ref{gplv2-private-modification} of this tutorial for more on this issue.)