This summary of facts from a recent case – United States v. O’Rourke, 2007 WL 104901 (U.S. District Court for the District of Arkansas – gives you an idea how this works:
Defendant O'Rourke came to the attention of the FBI on January 3, 2005, when Special Agent Robin Andrews conducted an undercover investigation of people involved in the possession and distribution of child pornography. . . . Conducting a search through the peer-to-peer Internet file sharing software known as `Limewire,’ Agent Andrews downloaded images of child pornography from Defendant's computer. . . . The FBI was able to identify Defendant through his Internet Protocol address and a subpoena of his Internet Service Provider, and subsequently obtained a search warrant for Defendant's home and computer. . . . The search warrant was executed on February 22, 2005, and Defendant's computer was found to contain 46 movie files and several hundred still images of child pornography. . . . The Government alleges that these movies and images were saved on Defendant's hard drive and were available to be downloaded over the Internet by others using Limewire software. . . .Here’s a summary of what happened in a similar case involving a search by a state officer:
The Government seized Defendant's computer and presented evidence to a federal grand jury. The grand jury indicted Defendant. . . .
[T]his case began on February 28, 2005, when at 4:35 p.m., Trooper Robert Erderly of the Pennsylvania State Police was logged onto a computer located at the Pennsylvania State Police barracks in Indiana, Pennsylvania. . . .United States v. Abraham, 2006 WL 3052702 (U.S. District Court for the Western District of Pennsylvania 2006).
Installed on the computer. . . was a file-sharing software program called Phex. Trooper Erdely used the Phex program to search for files on the Gnutella network.. BearShare and LimeWire are other such file-sharing software programs. . . .
The Gnutella network, BearShare, Phex and LimeWire share all types of files, including music, movie, photograph/still image, and text files. . .
On February 28 2005, the defendant, Arthur Abraham, was logged on to his computer at his residence at 3129 West Queen Lane, Philadelphia, Pennsylvania, and running a peer-to-peer file-sharing program called BearShare, version 4.6.3. . . .Once BearShare is installed, any file a person chooses to share is available to anyone on the Gnutella network. Every computer that is running this Gnutella network can participate in the sharing of the files. In order to install . . . the BearShare program . . . the defendant had to have accepted the terms of an end user software licensing agreement. With this agreement, the user acknowledges that he is using a file sharing program which can be used both to download files and to send files out over the Internet, i.e. share files. . . .
Returning to . . . February 28, 2005, the. . . defendant had to have his computer on and be using the "share the files in the library" option . . . when Trooper Erdely did his search because Trooper Erdely found the file being shared and was able to download it from the defendant's computer. . . .
Trooper Erdely knew that there was a movie file that was being shared across the Internet which is named Hindoo. Utilizing the Phex program, he searched the word Hindoo and got a number of hits. Once the result of Trooper Erdely's search came up, the Internet Protocol ("IP") addresses of those sharing the files on which Trooper Erdely got a hit were visible.
One of the IP addresses from one of Trooper Erdely's hits was an IP address belonging to Verizon Internet service. The IP was 184.108.40.206. . . . The complete name of the file being shared by IP 220.127.116.11 was (Hussyfan)(pthc) (r@ygold) (babyshivid) Hindoo4.mpg. Exhibit 5, unnumbered page 2.
Trooper Erdely obtained a state court order compelling Verizon to tell him who was the subscriber with the IP address 18.104.22.168. Verizon informed Trooper Erdely that the subscriber of that service at that date and time was . . . Arthur Abraham of 3129 West Queen Lane, Philadelphia, Pennsylvania 19129.
Trooper Erdely downloaded the file "Hindoo" that IP address 22.214.171.124 was sharing onto a CD Rom. The file on the CD Rom that Trooper Erdely downloaded from IP address 126.96.36.199 contains child pornography as prohibited by law. . . .
On March 17, 2005, a warrant was obtained to search the defendant's house at 3129 West Queen Lane, Philadelphia, Pennsylvania 19129. . . .
I find many things interesting about how law enforcement officers are using file-sharing programs to hunt for child pornography, but the one I want to focus on here wasn’t raise in the opinions in either of these cases, nor was it raised in the four other similar cases that are reported in Westlaw.
The issue is the Fourth Amendment which, as I’ve noted before, protects us from the government’s conducting “unreasonable” searches and seizures. The issue that would determine the applicability of the Fourth Amendment to the conduct of Agent Andrews and Trooper Erdely is whether what they did resulted in a “search” or a “seizure.”
As I’ve said before, a Fourth Amendment search is law enforcement’s intruding into a place, or an activity, in which the person has a “reasonable expectation of privacy.” You have a reasonable expectation of privacy in a place – your home, say – if (a) you think it’s private (subjective expectation) and (b) society agrees it is reasonable for you to think that (objective expectation). The home, of course, is clearly private – we all think our homes are private and our society emphatically agrees. That doesn’t mean law enforcement officers can’t search our homes; it just means they have to get a search warrant to do so.
The computers in both of these cases were in homes. Was it, then, a search for the law enforcement officers to access the hard drives on the computers to locate and copy a file or files (which, arguably, is a seizure)?
On the one hand, you could argue it was a search because we have an intrusion – a virtual kind of intrusion – by law enforcement into someone’s home. On the other hand, you can argue this is not a search because O’Rourke and Abraham both “opened the door” for law enforcement officers to “enter” their computers by installing and using the file-sharing software.
That is, as to the second argument, you can argue that (a) neither O'Rourke nor Abraham could have had a subjective expectation of privacy in their hard drives because they knew they were using file-sharing software and were online and (b) regardless of what they thought, society would not accept the notion that their hard drives were private given their use of that software. Society, in other words, would see their using the file-sharing software as the equivalent of my (hypothetically) putting my favorite marijuana plant (purely hypothetical) on a table next to the large window on the front of my house and pulling back the curtains so it could get plenty of sun. It would not be a search for a police officer to walk by and see the marijuana plant -- I gave up any expectation of privacy I had with regard to the plant by putting it on public display.
I assume none of the defendants raised the Fourth Amendment argument because they thought it would fail . . . or maybe they did raise it unsuccessfully and the courts simply did not issue a published opinion on that issue. I can see why the second argument would probably prevail . . . there's a long line of cases which say that if you engage in criminal activity with other people, don't complain if one of them turns out to be a snitch or, worse yet, an undercover FBI agent.
It seems to me, thought, that the second argument against law enforcement's using file-sharing software to explore people's hard drives raises a larger, perhaps more difficult issue: If I link my computer to a network, have I lost any Fourth Amendment expectation of privacy in the contents of my hard drive?