In a company blog post entitled "The Trouble with Tor," CloudFlare CEO Matthew Prince says that 94 percent of the requests the company sees coming across the Tor network are "per se malicious." He explains:
"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."