  Tor is widely used for staying anonymous online and accessing onion websites;
unfortunately, Tor is popular for distributing and viewing illicit child sexual
abuse material (CSAM). From 2018 to 2023, we analyse 176,683 onion domains and
find that one-fifth share CSAM. We find that CSAM is easily available using 21
out of the 26 most-used Tor search engines. We analyse 110,133,715 search
sessions from the Ahmia.fi search engine and discover that 11.1% seek CSAM.
When searching CSAM by age, 40.5% search for 11-year-olds and younger; 11.0%
for 12-year-olds; 8.2% for 13-year-olds; 11.6% for 14-year-olds; 10.9% for
15-year-olds; and 12.7% for 16-year-olds. We demonstrate accurate filtering for
search engines, introduce intervention, show a questionnaire for CSAM users,
and analyse 11,470 responses. 65.3% of CSAM users first saw the material when
they were children themselves, and half of the respondents first saw the
material accidentally, demonstrating the availability of CSAM. 48.1% want to
stop using CSAM. Some seek help through Tor, and self-help websites are
popular. Our survey finds commonalities between CSAM use and addiction.
Help-seeking correlates with increasing viewing duration and frequency,
depression, anxiety, self-harming thoughts, guilt, and shame. Yet, 73.9% of
help seekers have not been able to receive it.
