SAN FRANCISCO — The Justice Department’s aggressive steroids probe has led the Ninth Circuit U.S. Court of Appeals to enunciate a new set of Fourth Amendment protections for the digital age.

In an en banc opinion Wednesday that split conservatives on the court, Chief Judge Alex Kozinski said federal agents were wrong to seize swaths of drug test results from labs in Nevada and California. The computer files taken by the government revealed information about far more people — including baseball players and others — than allowed by a search warrant.