There has been an alarming growth in law enforcement's search of Google user data. Keyword warrants seek to identify every user who searched for a specific keyword, phrase or address. Geofence warrants compel disclosure of all devices in a geofenced area – such as a crime scene.
Such blanket warrants circumvent constitutional checks on police surveillance. Frequently, courts have ordered Google and other search firms to provide an accused's search history and location data. In those cases a specific person is suspected of a crime, but with a keyword search warrants reverse this and raise threats to individuals' privacy. Keyword searches will return hundreds, thousands, perhaps even millions of individuals who searched for information which is subject to the keyword warrant. As a result, many users will be caught up in the search even though the vast majority of those users will likely be completely innocent.
Keyword searches fail the particularity requirement of the Fourth Amendment to the United States Constitution. Law enforcement's inability to particularly describe probable cause for treating each Google user who searched for identified keywords forms the basis for such unconstitutionality.
Geofence warrants are even more chilling. There is zero particularity with regard to those warrants. Results are sought for every user within a particular distance from a named location.
Using private browsers can help to protect innocent users from such overbroad searches by law enforcement of private citizens. These, however, won't prevent valid investigations where a user has been identified as a suspect in a crime.