The full extent of an unprecedented FBI effort to beat the criminal underworld at its own encrypted-communications game became clearer Tuesday following a two-day takedown, with some 800 arrests worldwide and San Diego racketeering indictments against 17 high-level targets, according to federal authorities. Dubbed Operation Trojan Shield, the effort was largely led by FBI agents and federal prosecutors in San Diego who covertly created a closed-loop encryption cellphone service, called ANØM, and then convinced trusted voices already embedded in criminal syndicates to distribute the customized phones. The agents secretly read each message that poured in — 27 million in all....