  Shadow libraries, also known as ''pirate libraries'', are online collections
of copyrighted publications that have been made available for free without the
permission of the copyright holders. They have gradually become key players of
scientific knowledge dissemination, despite their illegality in most countries
of the world. Many publishers and scientist-editors decry such libraries for
their copyright infringement and loss of publication usage information, while
some scholars and institutions support them, sometimes in a roundabout way, for
their role in reducing inequalities of access to knowledge, particularly in
low-income countries. Although there is a wealth of literature on shadow
libraries, none of this have focused on its potential role in knowledge
dissemination, through the open access movement. Here we analyze how shadow
libraries can affect researchers' citation practices, highlighting some
counter-intuitive findings about their impact on the Open Access Citation
Advantage (OACA). Based on a large randomized sample, this study first shows
that OA publications, including those in fully OA journals, receive more
citations than their subscription-based counterparts do. However, the OACA has
slightly decreased over the seven last years. The introduction of a distinction
between those accessible or not via the Scihub platform among
subscription-based suggest that the generalization of its use cancels the
positive effect of OA publishing. The results show that publications in fully
OA journals are victims of the success of Sci-hub. Thus, paradoxically,
although Sci-hub may seem to facilitate access to scientific knowledge, it
negatively affects the OA movement as a whole, by reducing the comparative
advantage of OA publications in terms of visibility for researchers. The
democratization of the use of Sci-hub may therefore lead to a vicious cycle,
hindering efforts to develop full OA strategies without proposing a credible
and sustainable alternative model for the dissemination of scientific
knowledge.
