The FBI is denying that it paid $1 million to Carnegie Mellon University to exploit a vulnerability in Tor.

"The allegation that we paid [Carnegie Mellon University] $1 million to hack into Tor is inaccurate," an FBI spokeswoman told Ars in a Friday morning phone call.

Two days ago, the head of the Tor Project accused the FBI of paying Carnegie Mellon computer security researchers at least $1 million to de-anonymize Tor users and reveal their IP addresses as part of a large criminal investigation.

The FBI spokeswoman Ars spoke with declined to respond to further questions, advising us to send a followup e-mail and to contact Carnegie Mellon, which we did. Neither Carnegie Mellon nor the FBI has immediately responded to our inquiries. For now, it's not clear from the FBI's statement which part is inaccurate: the specific payment amount or its involvement entirely.

The Tor Project has also not immediately responded to Ars’ question as to whether it stands by its accusations. The organization has yet to offer any proof or substantiation of its claims.

One of the revealed Tor-masked IP addresses belongs to Brian Farrell, an alleged Silk Road 2 lieutenant who is due to stand trial in federal court in Seattle later this month. A new filing in Farrell's case, which was first reported Wednesday by Vice's Motherboard, says that a "university-based research institute" aided government efforts to unmask Farrell.

The Tor Project has since patched this vulnerability.