A federal appellate court further ironed out the reach of the Fourth Amendment in today's digital age, ruling the protection from unreasonable search and seizures does not apply to law enforcement's use of wireless-tracking software through a third-party internet router.

A panel for the U.S. Court of Appeals for the Ninth Circuit ruled Monday that the FBI's usage of software called Moocherhunter to find device addresses linked to child pornography did not constitute an unreasonable search under the Fourth Amendment since the suspect was pirating his neighbor's internet.

The defendant, Alexander Nathan Norris, allegedly used an unauthorized connection to his neighbor's wireless router to distribute child pornography through a peer-to-peer file-sharing network. The FBI deployed Moocherhunter, a software program aimed at identifying network trespassers without directly accessing any devices, via Norris' neighbor's network. Since the officers did not "physically intrude" on his residence, the act is not covered by constitutional protections, the court ruled.

Judge Johnnie Rawlinson, who wrote the opinion on behalf of Judges Mary Schroeder and Diarmuid O'Scannlain, compared the FBI's actions in the case to observing the source of loud music from within an apartment complex. 

"Although the music is produced within the apartment, the sound carries outside the apartment," Rawlinson wrote. "Just as no physical intrusion 'on constitutionally protected areas' would be required to determine the source of the loud music, no physical intrusion into Norris's residence was required to determine the strength of the wireless signal emanating from the devices in his apartment."

The court further ruled that the Fourth Amendment did not apply because Norris co-opted the neighboring apartment's wireless network. The panel cited a Third Circuit decision that also used Moocherhunter: United States v. Stanley. The defendant in that case also accessed child pornography through a third-party router, and the court decided that "while Stanley may have justifiably expected the path of his invisible radio waves to go undetected, society would not consider this expectation legitimate given the unauthorized nature of his transmission."

The Ninth Circuit largely agreed with the Stanley ruling, arguing that Norris forfeited his Fourth Amendment right when he illegally accessed the wireless connection.

"Indeed, it strains credulity to suggest that society would be prepared to recognize an expectation of privacy as reasonable when an individual gains access to the internet through the unauthorized use of a third-party's password-protected router located outside his residence," Rawlinson wrote.

Norris' attorney at appeal, John Balazs of The Law Office of John Balazs, declined to comment. 

The Department of Justice was represented by Assistant U.S. Attorneys Matthew Morris; Shelley Weger; Appellate Chief Camil Skipper; and McGregor Scott from the Eastern District of California. They did not immediately respond to a request for comment.