CIPAV, said the agent in the affidavit, would "cause any computer -- wherever located -- to send network-level messages containing the activating computer's IP address and/or MAC address, other environmental variables and certain registry-type information to a computer controlled by the FBI."

However, the warrant application did not spell out whether the CIPAV captured keystrokes or injected other code into the compromised system, as do commonplace Trojan downloaders. "The exact nature of [the CIPAV's] commands, processes, capabilities and their configuration is classified as a law enforcement sensitive investigative technique," said the 2007 document.

In Kelly's case, said Wired.com, the FBI was granted a warrant to use CIPAV on Feb. 10, 2005. Later that year, Kelly pleaded guilty to extortion, and was sentenced to five years probation and ordered to pay Verizon $378,000 for the damage he did.

According to the complaint filed against Kelly, he believed that "companies like Comcast and Verizon were indirectly responsible for his unemployment and dire financial situation because they worked with companies that favored foreign engineers over their counterparts and because they had indirectly stolen his intellectual property."

As part of his sentence in late 2005, Kelly was also ordered to enter a mental health program.