It’s a very good question, one I have debated with people at various meetings and with students in my classes.
To answer it I want to use a decision issued by a federal district court in Oklahoma a few weeks ago. The case is U.S. v. Breese, 2008 WL 1376269 (April 9, 2008). The opinion doesn’t seem to be available via the court’s website, so I’ll summarize it.
According to the opinion, Special Agent Scott Gibson, an officer with the FBI Cybercrimes Task Force
utilized LimeWire to search the internet using a search term known to be associated with child pornography files and then used a `browse host’ function of LimeWire to look at names of other shared files available on the same computer as a file in the search result. From file names suggesting child pornography, Agent Gibson selected files to download and, after viewing them, confirmed that they did contain images of child pornography. Agent Gibson subsequently used an administrative subpoena to identify the subscriber for the Internet Protocol (IP) address associated with the computer, which was Defendant's father, and then obtained a search warrant for the residence occupied by Defendant, his parents, and his girlfriend.
U.S. v. Breese, supra. Mr. Breese was obviously charged with possessing child pornography, though the opinion doesn’t describe the exact charged.
Mr. Breese moved to suppress the evidence seized from his home, arguing that the search warrant was the product of an “unlawful search of his personal computer by accessing files on it” using LimeWire. If police violate the 4th Amendment by conducting an unlawful search and then use evidence they obtained as a result of that unlawful search, the warrant is no good and any evidence obtained as a result of executing the warrant has to be suppressed. So if Mr. Breese could should that the agent’s accessing the files on his home computer was a “search,” he could have the evidence suppressed and, I suspect, the case would be dismissed.
The court held a hearing on the motion to suppress. At the hearing, an Oklahoma Highway Patrol officer, Captain Jeffrey Elliott, testified that
LimeWire is a computer program that permits users to establish a direct connection via the internet between two computers and to share files located on those computers, unless the file-sharing function is disabled. In other words, when a computer with peer-to-peer file sharing software like LimeWire is connected to the internet, the shared files on that computer are available to anyone else using compatible peer-to-peer software and connected to the internet; all users of the software can search the shared files on anther user's computer and gain entrance to those files via the internet.U.S. v. Breese, supra.
In ruling on the motion, the district court noted that for agent’s use of LimeWire to violate the 4th Amendment, it would have had to be a “search.” A “search” violates someone’s reasonable expectation of privacy in a place, such as the contents of one’s hard drive. In Katz v. U.S., 389 U.S. 347 (1967), the Supreme Court held that one has a reasonable expectation of privacy in a place if two conditions are met: (i) He thinks it is private; and (ii) society accepts his belief that the place is private as objectively reasonable.
When I teach this issue to my students, I use this hypothetical (just that) to illustrate how the two prongs of the Katz test work: I live in a small suburb, which has officers patrolling, sometimes, on bicycles. Assume, hypothetically, that I have a marijuana plant in my house and I want it to get some sun. I put it on a table in front of the large, uncurtained picture window in the front of my house, a picture window that is only about 25 feet from the sidewalk in front of my house. I leave it there while I go to work. An officer rides down the sidewalk on his bike and sees the marijuana plant; this gives him probable cause (!) to believe there is evidence of a crime (drug possession) in my house. He uses that to get a search warrant, enters the house, seizes the marijuana plant and I am, hypothetically (keep that in mind), charged with possession of an unlawful substance.
Like Mr. Breese, I (hypothetically) move to suppress the evidence, arguing that it was a “search” for the officer to observe the plant because it was in my home, which is the most private of 4th Amendment places. I will say I firmly believed it was private because it was in my home, and the court may buy that.
But even if the court accepts that I believed the plant was private, it will hold that the officer’s observing the plant was not a “search” under the 4th Amendment because society does not regard my belief as objectively reasonable. The court will hold that society does not regard my belief as objectively reasonable because ANYone walking down the sidewalk could have seen the plant; I took no steps, at all, to shield it from public view. For society to regard my belief that the plant in my home was private, I would have had to do something . . . put curtains on the window, for example.
That is exactly what the federal district court held in U.S. v. Breese:
The Court finds that, notwithstanding any subjective expectation that Defendant may have had in the privacy of his computer, it was not reasonable for him to expect privacy in files that were accessible to anyone else with LimeWire . . . software and an internet connection. This is not unlike the personal computer that the defendant in United States v. Barrows, 481 F.3d 1246 (10th Cir.2007), networked to a workplace computer for the purpose of sharing files. The court of appeals stated that, even though the defendant invited no one else to use his computer and may have expected its contents to remain private, `his failure to take affirmative measures to limit other employees' access makes that expectation unreasonable.’ . . . . Similarly, Defendant here had no Fourth Amendment expectation of privacy in files on his computer which were open to anyone connected to the internet to access via peer-to-peer file sharing.U.S. v. Breese, supra.
In other words, Mr. Breese loses because he didn’t put curtains on the window. It presumably follows that someone who uses LimeWire or any other P2P network DOES have a reasonable expectation of privacy in files they have not designed as private by disabling the file-sharing function.