Abstract: We provide detailed measurement of the illegal trade in child exploitation material (CEM, also known as child
pornography) from mid-2011 through 2014 on five popular peer-to-peer (P2P) file sharing networks. We characterize several
observations: counts of peers trafficking in CEM; the proportion of arrested traffickers that were identified during the investiga-
tion as committing contact sexual offenses against children; trends in the trafficking of sexual images of sadistic acts and infants
or toddlers; the relationship between such content and contact offenders; and survival rates of CEM. In the 5 P2P networks
we examined, we estimate there were recently about 840,000 unique installations per month of P2P programs sharing CEM
worldwide. We estimate that about 3 in 10,000 Internet users worldwide were sharing CEM in a given month; rates vary per
country. We found an overall month-to-month decline in trafficking of CEM during our study. By surveying law enforcement we
determined that 9.5% of persons arrested for P2P-based CEM trafficking on the studied networks were identified during the
investigation as having sexually offended against children offline. Rates per network varied, ranging from 8% of arrests for
CEM trafficking on Gnutella to 21% on BitTorrent. Within BitTorrent, where law enforcement applied their own measure of
content severity, the rate of contact offenses among peers sharing the most-severe CEM (29%) was higher than those sharing
the least-severe CEM (15%). Although the persistence of CEM on the networks varied, it generally survived for long periods of
time; e.g., BitTorrent CEM had a survival rate near 100%