“I believe this is the largest campaign we’ve seen that has been focused on drone technology,” said Darien Kindlund, manager of threat intelligence at the company, FireEye, based in California. “It seems to align pretty well with the focus of the Chinese government to build up their own drone technology capabilities.”

The hacking operation, conducted by a group called “Comment Crew,” was one of the most recent signs of the ambitions of China’s drone development program. The government and military are striving to put China at the forefront of drone manufacturing, for their own use and for export, and have made an all-out push to gather domestic and international technology to support the program…

Military analysts say China has long tried to replicate foreign drone designs. Some Chinese drones appearing at recent air shows have closely resembled foreign ones. Ian M. Easton, a military analyst at the Project 2049 Institute in Virginia, said cyberespionage was one tool in an extensive effort over years to purchase or develop drones domestically using all available technology, foreign and domestic.

Chinese engineers and officials have done reverse engineering, studied open source material and debriefed American drone experts who attend conferences and other meetings in China. “This can save them years of design work and mistakes,” Mr. Easton said.