The request by the FBI came in a case involving federal bank fraud and identity theft. The FBI had no idea where the suspect was, but they wanted to surreptitiously install software on their computer to find them.
The judge outlined the FBI's request writing that investigators wanted to “surreptitiously install data extraction software on the Target Computer. Once installed, the software has the capacity to search the computer’s hard drive, random access memory, and other storage media; to activate the computer’s built-in camera; to generate latitude and longitude coordinates for the computer’s location; and to transmit the extracted data to FBI agents within the district.”
Basically, this would give remote access to FBI agents to the suspect's computer, including the use of their webcam to spy on them.
“Hacking should be something that is the last resort, not the first option,” Chris Soghoian of the ACLU told Ars Technica.
Because the the FBI only has the IP address of the subject (which is actually one outside of the U.S.), the judge doesn't think the warrant request fulfills the fourth amendment requirement of a specific “place to be searched, and the persons or things to be seized.”
The judge wrote:
What if the Target Computer is located in a public library, an Internet café, or a workplace accessible to others? What if the computer is used by family or friends uninvolved in the illegal scheme? What if the counterfeit e-mail address is used for legitimate reasons by others unconnected to the criminal conspiracy? What if the e-mail address is accessed by more than one computer, or by a cell phone and other digital devices? There may well be sufficient answers to these questions, but the Government’s application does not supply them.