Court documents that surfaced in a Florida case against an alleged seller of counterfeit credit cards have shown that the FBI has a copy of servers that belonged to Tor Mail, a secure e-mail service that operated on the anonymous Tor network.

"Tor Mail's goal is to provide completely anonymous and private communications to anyone who needs it," states an informational page about the service, which remains up. "We are anonymous and cannot be forced to reveal anything about a Tor Mail user."

The information is found in a sworn statement by a US postal inspector and was reported by Wired's Kevin Poulsen this morning. The document explains that as part of the investigation, law enforcement collected orders for the fake credit cards that went through the e-mail address "platplus@tormail.net." That address contained every order for credit cards sent over the course of nearly a year.

In the document, postal inspector Eric Malecki explains that Tor Mail was "frequently used by individuals engaged in criminal activity to avoid detection by law enforcement because it allowed users to conceal their true identities and geographic locations." He continues:

Between July 22, 2013 and August 2, 2013, in connection with an unrelated criminal investigation, the FBI obtained a copy of a computer server located in France via a Mutual Legal Assistance Treaty request to France, which contained data and information from the Tor Mail e-mail server, including the content of Tor Mail e-mail accounts... Search of the Platplus Tor Mail Account revealed approximately 1,140 Website Order e-mails, dated from on or about September 9, 2012 through August 1, 2013, which were sent to both the Platplus Tor Mail Account and the Budlighthouse Gmail Account.

Tor Mail stopped working on August 4. As Poulsen notes, that alarmed many, including Dread Pirate Roberts, the operator of the Silk Road drug marketplace. "I personally did not use the service for anything important and hopefully neither did any of you," he wrote to his supporters.

Ross Ulbricht, whom the FBI has fingered as Dread Pirate Roberts, was arrested in October.

The Florida case involves three Florida men alleged to have run fakeplastic.net, a supply shop for fake credit cards and holographic stickers. The site began urging its users to switch to paying using Bitcoin in May 2013, as other payment systems like Liberty Reserve were being shut down.

"I strongly urge everyone who is working in our line of work to start using Bitcoin," wrote an admin on the site in a page captured and submitted in court documents by law enforcement. "Bitcoin cannot be shutdown by any person or government, it cannot track your ass down, it is anonymous and safe! It is why SllfRoad [sic] (largest drug buying marketplace) has always used Bitcoin as a payment processor."

The Tor Mail reveal comes at a time when secure e-mail services have been in the spotlight. In the wake of the Snowden investigation, the FBI apparently asked for private SSL keys from secure e-mail service Lavabit. But rather than provide them, its founder, Ladar Levison, shut down the service and appealed the ruling. His case is scheduled to be argued in the US Court of Appeals for the 4th Circuit this week.