WASHINGTON—The Federal Bureau of Investigation's top cyber cop offered a grim appraisal of the nation's efforts to keep computer hackers from plundering corporate data networks: "We're not winning," he said.

Shawn Henry, who is preparing to leave the FBI after more than two decades with the bureau, said in an interview that the current public and private approach to fending off hackers is "unsustainable.'' Computer criminals are simply too talented and defensive measures too weak to stop them, he said.

His...