In the twentieth century, the Supreme Court has set forth two distinct paradigms for interpreting the nature and limits of the Fourth Amendment. Until the late 1960s, the Court grounded its regulation of government searches in the concept of "constitutionally protected areas." [FN37] Under this view, the Court perceived the Fourth Amendment as a bright-line, property-based standard that required a warrant, supported by probable cause, for most physical trespasses onto private land. [FN38] However, in the years following its 1961 decision in Mapp v. Ohio [FN39] to vastly widen the scope of the Amendment by applying the exclusionary rule to state police officers, the Court came to recognize that the bright-line standard provided too limited a *1101 realm of protection from government searches. In three landmark cases, Katz v. United States, [FN40] Camara v. Municipal Court, [FN41] and Terry v. Ohio, [FN42] the Court revised its approach to the Fourth Amendment and attempted to articulate a standard that directly incorporated the values that inhered in a "constitutionally protected area." The resulting balancing method replaced the use of property as a central value, developing instead a values-focused test that weighs the government's interest in a search against the potential for police abuse of discretion and the threat to an individual's privacy inherent in the search.

This part explores the probable status of the Net-wide search first under the bright-line test of the pre- Katz Court and then under the current balancing approach. This review of the relevant case law demonstrates that the Net-wide search for digital contraband would be per se unreasonable under the "constitutionally protected areas" standard, and yet per se reasonable under the Court's balancing test as currently formulated. If this analysis is correct, one must ask whether the case of the Net-wide search is nothing more than a very anomalous case in which the pre- Katz standard would have provided too much protection, or whether there are in fact potentially important interests implicit in the Fourth Amendment that the Court has thus far failed to include in its balancing test.

In the Supreme Court's first significant examination of the Fourth Amendment, Boyd v. United States, [FN43] the Court found the protection of property to represent the core of the Amendment. In Boyd, the firm of E.A. Boyd and Sons was accused of claiming thirty-five more cases of plate glass as exempt from customs duties than it had actually used in constructing federal buildings; [FN44] the Court faced the question of whether the government could subpoena Boyd's papers for use against the firm. Writing for a majority of seven, Justice Bradley traced the history of the British use of the writs of assistance, by which officers of the Crown were empowered "in their discretion, to search suspected places for smuggled goods." [FN45] After explaining that the opposition to such sweeping and suspicionless searches was "perhaps the most prominent event which inaugurated the resistance of the colonies," [FN46] *1102 Justice Bradley went on to conclude that the protection of an individual's property interest served to restrict "all invasions on the part of the government and its employees of the sanctity of a man's home and the privacies of life." [FN47] The Court found that the papers were Boyd's property, and that Boyd alone was entitled to possess them. [FN48] Even against a "search" as targeted and minimally intrusive as a subpoena, the Court found that one's private property interest outweighed the government's interest in prosecuting crime. [FN49]

Although later decisions retreated to some extent from Boyd's absolute protection of private property, [FN50] they retained its property-based orientation. In a series of cases beginning with Hester v. United States, [FN51] the Court mapped out a variety of "constitutionally protected" locations. [FN52] Under this approach to the Fourth Amendment, government agents might freely inspect any unprotected area, but save for a "few specifically established and well-delineated exceptions," [FN53] official intrusion into a protected area required a warrant supported by probable cause.

The property-based model of the Fourth Amendment is well illustrated by Olmstead v. United States, [FN54] a 1928 case that arguably represented the Court's first foray into the jurisprudence of cyberspace. [FN55] In Olmstead, the Court held that federal agents had not violated the Fourth Amendment when they tapped the home and office phones of a suspected bootlegger. [FN56] A warrant was not necessary for a wire tap, wrote Chief Justice Taft, in large part because "the intervening wires [where the tap was placed] are not part of [the suspect's] house or office." [FN57] So long as government agents had not pierced the physical borders of the home or office, the Fourth Amendment accorded Olmstead no protection.

Applying the same trespass model over three decades later in Silverman v. United States, [FN58] the Court found that the Fourth Amendment had been violated by the insertion of a microphone into an individual's basement heating duct. This small insertion effectively turned the whole heating system into a house-wide microphone. Noting that "the eavesdropping was accomplished by *1103 means of an unauthorized physical penetration into the premises occupied by the petitioners," [FN59] the Court found that the penetration converted the eavesdropping into a violation of the Fourth Amendment. This physical intrusion into a protected physical sphere was, for the Court, the decisive difference between Olmstead and Silverman.

Silverman makes clear that under the property-based standard, a Net-wide search could not withstand Fourth Amendment scrutiny. Any governmental conduct that intruded, even minimally, into a constitutionally protected area without a warrant would violate the Amendment's mandate. The fact that the officer himself is outside the zone would be no more relevant for the Net-wide search than it was for the Court in Silverman; the intrusion of the government's search program into the sanctity of a private home or office would trigger the need for probable cause. And the Net-wide search, in invading a subject's hard drive and momentarily seizing control of the computer to execute its scan, would constitute such an intrusion.

The Net-wide search by its very nature precludes a probable cause justification for the intrusion. Because it is simpler and more effective to physically seize a suspect's hard drive than to attempt to access it through the network, [FN60] an officer who possessed probable cause would secure a traditional warrant for a traditional search. By contrast, law enforcement would use the Net-wide search only when seeking to identify unknown possessors of digital contraband. The search seeks to examine as many drives as it can access, and the likelihood of access bears no relation to the likelihood of illicit files. Under the bright-line test, such a search would be a search without individualized suspicion and -- by definition -- a violation of the Fourth Amendment.

In the late 1960s, the Court revised its bright-line approach and developed a balancing test that weighed the government's interest in a search against the costs of the search's invasion of individual privacy. The result, as Louis Seidman has noted, is that "[m]odern Fourth Amendment law focuses on what might be called the 'collateral damage' imposed by searches." [FN61] Collateral damage includes the involuntary disclosure of personal information not relevant to the investigation, as well as the "violence, disruption, and humiliation" [FN62] implicit in any search. When the Court speaks of a privacy interest in the context of the Fourth Amendment, it is almost certainly referring to an *1104 individual's interest in avoiding either collateral personal revelations or humiliating and potentially violent confrontations with agents of the government. By contrast, where the Court finds none of these collateral damages, it is unlikely to find a violation of privacy.

The Court initiated its revision of the bright-line approach when confronted with a series of cases in which that approach either would have allowed too much collateral damage or, by requiring that the government have probable cause, would have unreasonably hampered important social interests. In Katz v. United States, [FN63] the Court faced the question of whether a wiretap on a public phone was a violation of the Fourth Amendment. Rather than accept the conclusion of Olmstead and Silverman that the Fourth Amendment's supervision of collateral damage ends at the border of the home or office, the Court instead rejected the absolute line between those areas and the rest of the world. Justice Stewart explained that "[w]hat a person knowingly exposes to the public, even in his own home or office, is not a subject of Fourth Amendment protection. But what he seeks to preserve as private, even in an area accessible to the public, may be constitutionally protected." [FN64] Katz's phone conversation could not be intercepted without a warrant.

If Katz established that the traditional probable cause standard could apply outside the home and office, Camara v. Municipal Court [FN65] established that searches of the home need not always require probable cause if the intrusion is limited. Camara presented the question of whether a housing inspector required a warrant to enter an apartment against the tenant's wishes. Confronted with the municipality's argument that adherence to the traditional probable cause standard would significantly compromise the usefulness of housing inspectors, [FN66] the Court upheld the search. In light of the unique need for collective inspections and the "relatively limited invasion of privacy" [FN67] involved in searches targeted at buildings rather than individuals, the Court found that such an "inspection is a 'reasonable' search" of the home despite the lack of individualized suspicion. [FN68]

The third case, Terry v. Ohio, [FN69] presented the Court with the question of whether a police frisk implicated the Fourth Amendment. Had it chosen to maintain the traditional probable cause requirement, the Court either would have had to allow officers unlimited discretion to frisk (and potentially harass) or it would have had to require probable cause of an officer before he could make sure that a suspect was not armed. Again, the Court chose instead to *1105 modify the traditional test, explaining that "[t]he Fourth Amendment proceeds as much by limitations upon the scope of governmental action as by imposing preconditions upon its initiation." [FN70] In permitting frisks based on "articulable suspicion," [FN71] Terry tailored the level of suspicion required to the intrusiveness of the search. This tailoring, in turn, opened the way to a sliding scale in which, the less intrusive the search, the less demanding the procedural requirements for the search to be "reasonable."

Of course, the balancing standard developed in Katz, Camara, and Terry continued to provide the home and office with an exceptionally high level of protection. [FN72] The similarity of result -- and of rhetoric [FN73] -- should not obscure the change in doctrine; the same high level of protection provided by the balancing approach now follows from the fact that any entry into the home or office is virtually certain to impose significant collateral damage. As Professor Seidman notes, when the police conduct such a search, they will almost inevitably interfere with legitimate activity, disrupt personal belongings, and discover personal details that they have no right to learn. [FN74] Even in a case in which police did no more than place a tracking device inside an object to be brought into a home, which permitted the officers nothing more than the "[i]ndiscriminate monitoring of [the location of] property. .. withdrawn from public view," [FN75] the Court has found that the probability of collateral disclosure is significant enough to demand judicial oversight. [FN76] Private homes are areas that "deserve the most scrupulous protection from government invasion" in order to "protect those intimate activities that the Amendment is intended to shelter from government interference or surveillance." [FN77]

Nevertheless, although the Court occasionally proclaims that "searches and seizures inside a home without a warrant are presumptively unreasonable," [FN78] the presumption that a warrant is required can be rebutted if the Court finds that the social need for a search outweighs the damages it imposes. Camara *1106 was one such case. Griffin v. Wisconsin, [FN79] upholding the warrantless search of a probationer's home, was another. In Griffin, the Court explained that, although searches of the home are usually "undertaken only pursuant to a warrant. .. we have permitted exceptions when 'special needs, beyond the normal need for law enforcement, make the warrant and probable-cause requirement impracticable."' [FN80]

And here the remarkable feature of the Net-wide search for digital contraband becomes apparent: Despite the number of home and office systems searched and despite the total absence of particularized suspicion, the search would result in virtually no collateral damage as currently understood by the Court. There would be no frightening confrontation with authority, no possibility for abuse of discretion, and no disclosure of irrelevant information, private or otherwise, to the police. The Court has noted that "the problem [inherent in the general warrant] is not that of intrusion, per se, but of a general, exploratory rummaging in a person's belongings," [FN81] and the remarkable feature of the Net-wide search is that it allows an intrusion without the slightest meaningful rummaging. [FN82]

As a consequence, under current jurisprudence, such a search would unquestionably be "reasonable." While most balancing tests require the use of judgment and discretion to weigh the different elements, no balancing is required where all the weight is on one side. Even a casual government interest, much less than compelling, might justify this search.

Two decisions in particular, United States v. Place [FN83] and United States v. Jacobsen, [FN84] laid the foundations for this conclusion; together, these cases held that a minimally intrusive practice that reveals "only the presence or absence of. .. contraband" [FN85] is not recognized as a "search" by the Constitution and hence does not implicate Fourth Amendment scrutiny. The first of these cases, United States v. Place, addressed the question of a dog's sniffing of a suspect's luggage for narcotics. The Court noted that since such a sniff "does not require opening the luggage [and] does not expose noncontraband items that would otherwise remain hidden from public *1107 view.. .. the information [so] obtained is limited" to the revelation of contraband. [FN86] The Court continued:

In these respects, the canine sniff is sui generis. We are aware of no other investigative procedure that is so limited both in the manner in which the information is obtained and in the content of the information revealed by the procedure. Therefore. .. exposure of respondent's luggage. .. to a trained canine did not constitute a [Fourth Amendment] "search".. . . [FN87]

While some would have read this conclusion as resulting from the dog's use of odors outside the defendant's property, [FN88] the Court made clear the following year that the decisive fact was "that the governmental conduct [in Place] could reveal nothing about noncontraband items." [FN89] In Jacobsen, federal agents tested a small amount of a white powder that Federal Express employees had accidentally discovered in a package. The test destroyed the small sample, but it identified the substance as cocaine. In response to arguments that the test constituted a search, the Court explained that "governmental conduct that can reveal whether a substance is [contraband], and no other arguably 'private' fact, compromises no legitimate privacy interest." [FN90] As a consequence, the police are free to seek such contraband so long as their search "could, at most, have only a de minimis impact on any protected property interest." [FN91]

While this conclusion may seem a bright-line rule and a radical departure from the balancing test, it is instead the logical result of that test. A minimally intrusive governmental practice that can reveal only contraband by definition cannot have a recognized collateral effect and so cannot possibly be found unreasonable. While some judges and scholars have objected that being forced to submit to inspection by a large, panting dog inflicts cognizable harm, [FN92] this criticism is directed at the Court's interpretation of the intrusiveness factor rather than at the test's formulation. If one accepts the Court's implicit *1108 assumption that being sniffed by a dog involves neither confrontation nor collateral damage, such a search is per se reasonable. [FN93]

Unlike the confrontation between dog and target, there is no possible claim of collateral damage in the Net-wide search. As such, the consequence of the Court's reasoning in Jacobsen is clear. Since the Net-wide search has only a de minimis impact on the property interests of any individual [FN94] and reveals nothing "private" beyond the presence of digital contraband, the officers who ran the Net-wide program would not be conducting a Fourth Amendment search. The Court would even be relieved of the need to articulate a "special need" exception from the individualized-suspicion requirement since only "searches" require individualized suspicion.