I mentioned this awhile back when a similar topic came up. Awhile back I wrote a small crawler/search engine for onion sites that didn't log visitor info, just the search terms. After about a week if running I went back to see what people were searching for and the majority of it was child porn. I was totally shocked. I had anticipated cracking and warez type stuff but not child porn, or at least not at the levels I was seeing. I shut down the app after that :(