Tor, the anonymizing tool used by everyone from privacy advocates to drug dealers to dissidents, has apparently stopped the FBI from pursuing a potential child pornography bust on at least one occasion. A report recently released by the Department of Justice discusses how content on one of the largest anonymous "darknet" sites, Silk Road, was untraceable due to Tor. A user had reported finding an "adult" section that appeared to contain pictures of very young children, after which he wiped his hard drive. "Because everyone (all internet traffic) connected to the TOR network is anonymous," the report reads, "there is not currently a way to trace the origin of the website. As such no other investigative leads exist."

This incident, which apparently happened in late 2011, was one of several cases in which law enforcement had come up against Tor. What makes this somewhat unusual is the claim that Tor cut off the trail. Although cases have been stopped by it before, several other anonymous sites, most recently the "Farmer's Market," have been shut down and had their operators arrested despite using the tool, often because of other vulnerabilities. "Saying that you have no leads is ridiculous," Tor Project development director Karen Reilly told Ars Technica.