The Fourth Amendment in an E-World
CS593: Digital Forensics — D. Kevin McGrath
- The Fourth Amendment in an E-World
Overview
Any digital forensics investigation within the U.S. must respect privacy and search laws, starting with the Fourth Amendment. This lecture covers what the Fourth Amendment actually says (which differs from what many people think), how it applies in electronic contexts, exceptions to the warrant requirement, and how the law has struggled to address modern communications and data held by third-party providers.
What Is the Fourth Amendment?
The full text:
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
Key points from the text:
- It protects against unreasonable searches — not all searches. The Amendment doesn’t define “unreasonable”; courts have developed that interpretation over time.
- Warrants require probable cause: a high probability that evidence of a crime will be found.
- A search does not become reasonable merely because a warrant was obtained. A warrant is a procedural protection, not a retroactive justification.
- Warrants must specifically describe what is to be searched and seized. Blanket general warrants are prohibited.
Reasonable Expectation of Privacy
The modern interpretation grounds Fourth Amendment protection in expectation of privacy. The Supreme Court has articulated a two-part test:
- The person must have a subjective expectation of privacy — they must actually believe the thing in question is private.
- That expectation must be objectively reasonable — society in general would agree it is reasonable.
Example: Contents of a wastebasket inside your home → reasonable expectation. The same trash placed in a bag at the curb → no longer reasonable (it’s on the road for anyone to see).
The Fourth Amendment applies only to government action — it constrains prosecutors, police, and other government agents, not private citizens. If a landlord searches a tenant’s apartment, that’s not a Fourth Amendment issue (it’s a civil matter).
Electronic context: A password on a computer functions like a lock on a box — it is evidence of a subjective expectation of privacy. Whether that expectation is societally reasonable is the crux of many disputes about electronic evidence.
Encryption: When data is encrypted, there are ongoing legal disputes about whether the government can compel decryption. Courts have disagreed; outcomes depend on what the government already knows and what the suspect has said.
Exceptions to the Warrant Requirement
Normally, a lawful government search requires advance authorization from a judge (a warrant) supported by probable cause. However, there are recognized exceptions:
Consent
If the person whose property is to be searched consents — explicitly or implicitly — no warrant is needed. Consent can be:
- Explicit: a person agrees when police ask.
- Implicit: a university professor may implicitly consent to certain searches as a condition of employment.
Consent can also be given by a cotenant with apparent authority over the property (e.g., a spouse). The scope of consent matters; disputes about who consented and to what are common.
Exigent Circumstances
Exigent circumstances exist when there is a good reason to act immediately without waiting for a warrant:
- Evidence may be destroyed before a warrant can be obtained (automated deletion policies; remote wipe).
- A crime is in progress.
This exception is especially relevant to digital investigations, where electronic evidence can disappear rapidly.
Plain View
If investigators are lawfully present somewhere (on a valid warrant or otherwise) and encounter evidence of a crime in plain view, they may seize it without a separate warrant — as long as it is immediately apparent that the object is incriminating (Horton v. California, S. Ct. 1990).
Plain view applies whenever you are in a place you have a right to be, doing things you have a right to do.
Digital twist: If you seize a hard drive under a warrant for network intrusion and discover a folder named to suggest child pornography, plain view doctrine becomes complicated. Can you open the folder under the existing warrant? Most law enforcement will get a second warrant rather than proceed.
Privacy in an Electronic Context
Electronic environments create two recurring problems:
- Disputed reasonable expectation of privacy: What counts as private in an online or cloud-hosted context? Courts have been inconsistent.
- Third-party storage: When your data is stored by someone else (a service provider), Fourth Amendment protection may be reduced or eliminated under the third-party doctrine.
Email is the paradigmatic example. Is a web-based email account private like a postal letter? Or have users waived their privacy by agreeing to terms of service that allow the provider to scan messages for advertising purposes? Courts have disagreed.
Third-Party Doctrine
The core principle: When you share information with a third party, you accept the risk that the third party will share that information with someone else — including law enforcement.
- Hoffa v. United States: Hoffa bragged to a friend about jury tampering. The friend told police. The Court said Hoffa had no Fourth Amendment claim — he gave up his expectation of privacy by sharing.
- U.S. v. Miller (S. Ct. 1976): Financial records turned over to a bank in the ordinary course of business are not protected by the Fourth Amendment. No warrant needed to seize them.
The question for the internet: does sharing data with a service provider (often without realizing it) constitute voluntary disclosure sufficient to eliminate Fourth Amendment protection?
The Stored Communications Act (SCA)
The Stored Communications Act (1986), enacted before the World Wide Web, fills some gaps in Fourth Amendment coverage for electronic information. It creates three tools for compelling disclosure of stored communications:
| Tool | Standard |
|---|---|
| Search warrant | Probable cause |
| Subpoena | Reasonable relevance (lowest standard; very easy to obtain) |
| 2703(d) order | Specific and articulable facts showing records are relevant to an ongoing criminal investigation |
Under the SCA, a warrant is required for e-mails in electronic storage for less than 180 days. For e-mails older than 180 days, a 2703(d) order may suffice.
Baseline rule: If the circumstances require a warrant under the Fourth Amendment, a subpoena or 2703(d) order is not sufficient. A warrant is always acceptable even when it is not legally required.
United States v. Warshak (6th Cir. 2010)
Facts: Steven Warshak ran a company selling Enzyte (the “Smilin’ Bob” herbal supplement). He was convicted of mail fraud, wire fraud, and money laundering. Investigators obtained his e-mails — more than 180 days old, stored with service provider NuVox — using a 2703(d) order, without a warrant.
Sixth Circuit ruling: The Court held that Warshak had a reasonable expectation of privacy in his e-mails, analogous to paper letters, and that the SCA’s lower standard was constitutionally insufficient. A warrant was required. However, because investigators acted in good faith reliance on the SCA, the convictions were affirmed.
Significance: Warshak is not binding precedent outside the Sixth Circuit, and many other circuits have reached the opposite conclusion. The law in this area remains unsettled.
Cell Phone Geolocation Data
Cell providers store historic cell site location information (CSLI) — records of which towers a phone connected to. This metadata can reconstruct a suspect’s movements over time.
Two appellate courts initially reached opposite conclusions on whether obtaining CSLI requires a warrant or only a 2703(d) order:
- U.S. v. Graham (4th Cir.): 2703(d) order sufficient.
- U.S. v. Davis (11th Cir.): Warrant required.
U.S. v. Jones (S. Ct. 2012) involved GPS tracking of a suspect’s car. The Court held that physically attaching a GPS device to the car was a Fourth Amendment trespass — but declined to address the broader question of whether the data collected has Fourth Amendment protection.
Carpenter v. United States (S. Ct. 2018) resolved the circuit split. In a 5–4 decision, Chief Justice Roberts writing for the majority held that the government must obtain a warrant to access seven or more days of CSLI. The Court recognized that long-term location data is qualitatively different from the “business records” at issue in earlier third-party doctrine cases — its granularity and comprehensiveness means it provides “near perfect surveillance” of a person’s movements. Carpenter is now the controlling precedent on warrant requirements for historical CSLI.
Key tension: Metadata may feel less intimate than conversation content, but location data accumulated over time reveals far more about a person’s life — their routine, their relationships, when they deviate from the norm.
City of Ontario v. Quon (S. Ct. 2010)
A California police sergeant used a work-issued pager to send personal (“spicy”) messages. His employer (a police department — a government actor) obtained message content from the service provider without a warrant.
The case illustrates how courts often reason about technology from a position of incomplete understanding. Chief Justice Roberts, in oral argument, expressed surprise that messages sent to someone don’t “just go right to the other thing” — apparently unaware that messages pass through service providers. Courts deciding privacy rights of digital data often do not fully understand how digital data works.
Riley v. California (S. Ct. 2014)
Unanimous decision: Searching the contents of a cell phone incident to arrest requires a warrant. The “search incident to arrest” exception — which allows police to search a person and their immediate possessions when making an arrest — does not extend to the digital contents of a cell phone.
From the opinion:
“Modern cell phones are not just another technological convenience. With all they contain and all they may reveal, they hold for many Americans ‘the privacies of life.’ The fact that technology now allows an individual to carry such information in her pocket does not make the information any less worthy of the protection for which the Founders fought.”
Riley is a major Fourth Amendment decision, and the unanimous nature of the ruling is striking. The Court acknowledged that the analysis becomes more complicated when information is stored in the cloud (implicating third-party doctrine) rather than on the device itself.