  Bitcoin is a cryptocurrency attracting a lot of interest both from the
general public and researchers. There is an ongoing debate on the question of
users' anonymity: while the Bitcoin protocol has been designed to ensure that
the activity of individual users could not be tracked, some methods have been
proposed to partially bypass this limitation. In this article, we show how the
Bitcoin transaction network can be studied using complex networks analysis
techniques, and in particular how community detection can be efficiently used
to re-identify multiple addresses belonging to a same user.
