The opinion reverses a lower court ruling in which a U.S. District Court judge in Virginia suppressed the evidence, saying the government had violated a defendant's rights.
The decision stems from ain which a hacker uploaded a file to a child porn newsgroup that made it possible to track who downloaded files from the service. The uploaded file contained the SubSeven virus, which the hacker used to remotely search people's computers for porn.
The hacker then played the role of a cybervigilante, sending anonymous tips to law enforcement officials that alerted them to child porn files the hacker had found on people's PCs.
The attorneys for one of the men nabbed in the hacker's sting sued, saying that the hacker was acting as an agent of the government and therefore needed a warrant before conducting a search of someone's computer. A federal court judge ruled that the government had indeed violated the man's Fourth Amendment rights protecting him from unreasonable search and seizure.
However, an appellate panel of the Fourth Circuit Court of Appeals reversed that decision because, among other things, most of the major exchanges between law enforcement and the hacker took place after he had searched the man's computer. As a result, the judges said, the government had not established a relationship with the hacker prior to his search that would have made him an agent of the government.
"In order to run afoul of the Fourth Amendment, therefore, the government must do more than passively accept or acquiesce in a private party's search efforts," the judges wrote. "Rather there must be some degree of government participation in the private search."
However, the appellate judges warned that law enforcement "operated close to the line" in the case.