An anonymous reader writes: In early 2003, F.B.I. agents hit a roadblock in a secret investigation, called Operation Trail Mix. For months, agents had been intercepting phone calls and emails belonging to members of an animal welfare group that was believed to be sabotaging operations of a company that was using animals to test drugs. But encryption software had made the emails unreadable. So investigators tried something new. They persuaded a judge to let them remotely, and secretly, install software on the group’s computers to help get around the encryption. That effort, revealed in newly declassified and released records, shows in new detail how F.B.I. hackers worked to defeat encryption more than a decade before the agency’s recent fight with Apple over access to a locked iPhone. The Trail Mix case was, in some ways, a precursor to the Apple dispute. In both cases, the agents could not decode the data themselves, but found a clever workaround. The Trail Mix records also reveal what is believed to be the first example of the F.B.I. remotely installing surveillance software, known as spyware or malware, as part of a criminal wiretap. “This was the first time that the Department of Justice had ever approved such an intercept of this type,” an F.B.I. agent wrote in a 2005 document summing up the case.