The method used by the SEI may have also let other observers of the Tor network "hijack" SEI's information and de-anonymize Tor sites or users themselves.

SEI "had the ability to deanonymize a new Tor hidden service in less than two weeks," the source said. "Existing hidden services required upwards of a month, maybe even two months."

"The trick is that you have to get your attacking Tor nodes into a privileged position in the Tor network, and this is easier for new hidden services than for existing hidden services," the source, who asked to remain anonymous for fear of losing his or her job, continued.

On Wednesday, Motherboard reported that a "university-based academic research institute" had been providing information to the FBI, leading to the identification of criminal suspects on the dark web, including those allegedly involved with the now-defunct marketplace Silk Road 2.0, and a man charged with possession of child pornography.