It's explained in the article. On the other hand, anonymity is also something that provides value to online attackers. Based on data across the CloudFlare netw

It's explained in the article. On the other hand, anonymity is also something that provides value to online attackers. Based on data across the CloudFlare network, 94% of requests that we see across the Tor network are per se malicious. That doesn’t mean they are visiting controversial content, but instead that they are automated requests designed to harm our customers. A large percentage of the comment spam, vulnerability scanning, ad click fraud, content scraping, and login scanning comes via the Tor network. To give you some sense, based on data from Project Honey Pot, 18% of global email spam, or approximately 6.5 trillion unwanted messages per year, begin with an automated bot harvesting email addresses via the Tor network. Rate limiting would block legitimate users, and pow doesn't impede the malicious uses of tor.