Cloudflare services have been used by Rescator, a carding website that sells stolen payment card data.
In 2018, Cloudflare was identified by the European Union's Counterfeit and Piracy Watch List as a "notorious market" which engages in, facilitates, or benefits from counterfeiting and piracy. The report noted that Cloudflare hides and anonymizes the operators of 40% of the world's pirate sites, and 62% of the 500 largest such sites, and "does not follow due diligence when opening accounts for websites to prevent illegal sites from using its services." Italian courts have enjoined Cloudflare to cease hosting pirate television service "IPTV THE BEST" after it was found to be infringing the intellectual property of Sky Italy and the Italian football league, and German courts have similarly found that "Cloudflare and its anonymization services attract structurally copyright infringing websites."
Cloudflare has been cited in reports by The Spamhaus Project, an international spam tracking organization, for the high numbers of cybercriminal botnet operations hosted by Cloudflare. An October 2015 report found that Cloudflare provisioned 40% of the SSL certificates used by typosquatting phishing sites, which use deceptive domain names resembling those of banks and payment processors to compromise Internet users' banking and other transactions.
For detaiils, please see https://en.wikipedia.org/wiki/Cloudflare.