  Peer-to-peer (P2P) systems are widely used to exchange content over the
Internet. Knowledge on paedophile activity in such networks remains limited
while it has important social consequences. Moreover, though there are
different P2P systems in use, previous academic works on this topic focused on
one system at a time and their results are not directly comparable.
  We design a methodology for comparing \kad and \edonkey, two P2P systems
among the most prominent ones and with different anonymity levels. We monitor
two \edonkey servers and the \kad network during several days and record
hundreds of thousands of keyword-based queries. We detect paedophile-related
queries with a previously validated tool and we propose, for the first time, a
large-scale comparison of paedophile activity in two different P2P systems. We
conclude that there are significantly fewer paedophile queries in \kad than in
\edonkey (approximately 0.09% \vs 0.25%).
