Tor is celebrated by civil liberty and privacy groups for offering anonymity to whistleblowers and dissidents. But the service has also drawn criticism for being used not just for distributing child pornography, but also for onion sites such as Silk Road, which facilitates the buying and selling of narcotics.
Just how much of the Tor network facilitates illegal activities? Last month, three University of Luxembourg researchers who conducted a study of Tor hidden services reported that "while the content of Tor hidden services is rather varied, the most popular hidden services are related to botnets." Their report, titled "Content And Popularity Analysis Of Tor Hidden Services," is based on their use of a documented flaw -- now patched -- in Tor, which allowed them to count 39,824 unique onion addresses in February 2013.
Reviewing what appeared to be the 20 most popular Tor addresses, the researchers found that 11 -- including all of the top five sites -- were botnet command-and-control servers, while five provided adult content. Also on the top 20 list was Silk Road, which placed 18th, well ahead of Freedom Hosting (27th). Interestingly, the researchers even discovered a phishing site disguised as the Silk Road.
On balance, however, the researchers found a balance between licit and illicit sites. "The number of hidden services with illegal content or devoted to illegal activities and the number of other hidden services -- devoted to human rights, freedom of speech, anonymity, security, etc. -- is almost the same; among Tor hidden services one can even find a chess server," the researchers wrote.
As that suggests, many tools can be freely used by people with good or bad intentions. Former NSA and CIA director Michael Hayden said as much Sunday, when he delivered a talk on "the tension between security and liberty" that touched on the intelligence community's imperative to eavesdrop on some Gmail communications, The Washington Post reported.
"Gmail is the preferred Internet service provider of terrorists worldwide," said Hayden, who instead of "Internet service provider" most likely meant "email service."
Then again, the alleged use of Gmail by terrorists shouldn’t come as a surprise. "I don't think you're going to see that in a Google commercial, but it's free, it's ubiquitous, so of course it is" used that way, Hayden said.
Of course, Tor and Gmail are far from the only free tools to be used for illicit purposes. In July, notably, security researchers reported that Chinese groups have been using Dropbox to distribute malware for online espionage operations.