When a federal, state or local law enforcement agency wants to search somebody's home or property in Pittsburgh, they generally must get a search warrant first. The principle behind this is to prevent police from conducting random searches of people's homes with little to no pretext. Our nation was founded on the idea of limited police powers and the Fourth Amendment in the Bill of Rights helps enshrine this principle with its warrant requirement.
An important part of the warrant clause is meant to prevent obtaining a search warrant from the court from becoming a blank check to search anywhere and everywhere for evidence of a white collar crime or other type of crime. It requires the police to go into a sufficient level of detail of the "place to be searched, and the persons or things to be seized." The officers must show probable cause that the evidence is contained in the specified places to be searched or the court will not grant the warrant.
A federal magistrate recently denied the FBI's request to hack into the computer of a person they suspect of white collar crimes. Federal investigators had asked the judge for permission to install spyware on the suspect's computer for a month in order to search its hard drive and monitor him through his computer's video camera, among other things. The FBI appears not to know where the suspect is and could be in another country. In other words, it sought a warrant with worldwide range in order to hack into a computer that may or may not belong to the suspect.
The judge denied the warrant request. He said the FBI's scope was too vague and violated the Fourth Amendment's specificity requirement. He also noted that investigators could not be sure that the virus would reach the correct computer or infect a person not mentioned in the warrant request.
Source: Ars Technica, "FBI denied permission to spy on hacker through his webcam," Cyrus Farivar, April 24, 2013