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“We’re pretty sure we know who some of these people are,” Mr. McWhorter said.

He added, however, that it is hard to know what happened to the stolen information once it arrived in Shanghai. “Once the information has gotten back to the PLA, it is very difficult to track it,” he said. “It is a black box.”

Although no indictments for state-sponsored hacking have been made public, Mr. DuBose said, such documents generally are kept under seal until the alleged perpetrator can be arrested or otherwise apprehended.

“It’s possible that there are indictments out there already” but being kept under wraps in case the indicted suspects travel to America or a third country with an extradition treaty with the U.S., he said.

Mr. Baker suggested that another tack might be more profitable than waiting for senior Chinese military officials to take a vacation in the wrong country.

He advocated building cases against the companies that profited from the thefts — the state-owned or state-supported Chinese enterprises that were able to leapfrog their U.S. competitors by stealing their research and development.

“The companies [that benefit] are the softest targets and the easiest ones to reach,” Mr. Baker said, noting that any company that had received stolen data would be chargeable as a co-conspirator or accessory. Unlike senior PLA officers, “they must do business in jurisdictions other than China, in jurisdictions where they are reachable,” he said of such companies.

Besides the mention in Mr. Obama’s State of the Union address, the issue of cyberespionage also has elbowed its way into diplomatic and military relations between China and the U.S., according to the administration.

“We have repeatedly raised our concerns at the highest levels about cybertheft with senior Chinese officials, including in the military, and we will continue to do so,” said Ms. Hayden, the White House spokeswoman.

Federal prosecutors have charged companies that benefited from economic espionage by China — but so far, only of the offline variety.

In one case opened last year, prosecutors brought criminal conspiracy charges of economic espionage against five Chinese companies alleged to have obtained proprietary information about chemical processes from DuPont by bribing employees to steal it.

“To charge it as economic espionage,” said one federal official, prosecutors “have to show a government is behind it.”

This article is based in part on wire service reports.