Though relations between the two have warmed in recent years, Beijing has never recanted a vow to retake the island, by force if necessary.
Information about the U.S.-supplied defense systems could also help the People's Liberation Army understand other U.S. defenses. Taiwanese officials, however, say their systems are secure, and U.S. experts say American secrets will remain protected in any case.
The possibility that Taiwan might give up military secrets is certainly a worry for the U.S., its most important foreign partner.
Despite shifting recognition from Taipei to Beijing in 1979, Washington continues to sell the island sophisticated military equipment, and sees it as an element in a string of Asian defense relationships that stretches from South Korea to Australia. Any confirmed leak of U.S. defense secrets from Taiwan to China could undermine U.S. willingness to continue providing military equipment and technology to the island.
"We are concerned whenever this type of incident occurs," a U.S. defense official said in an email response to an Associated Press request for comment on the recent espionage incidents. "However, Taiwan has taken aggressive steps in the last year to protect itself from intelligence threats." The official spoke on condition of anonymity because of the sensitivity of the issue.