In Washington, officials criticize what they consider state-sponsored attacks. The officials say intrusions against foreign governments and businesses are growing, and the Pentagon this month accused the Chinese military of attacking American government computer systems and military contractors. The White House, which has ordered cyberattacks against Iran, has made cybersecurity a priority in talks with China. The Chinese Foreign Ministry says China opposes hacking attacks and is itself a victim.

The furor in Washington intensified in February after The New York Times and other news organizations published details of hacking efforts against their own networks and the findings of a new report by a cybersecurity company, Mandiant. The report said a shadowy group within the People’s Liberation Army, Unit 61398, ran a formidable hacking and espionage operation against foreign entities out of a building on the outskirts of Shanghai.

In China, the unit is just one part of the complex universe of hacking and cybersecurity. And the military units are not a well-kept secret. At least four former employees of Unit 61786, responsible for cryptography and information security, have posted résumés on job-search Web sites listing employment in the unit.

Another job seeker reported employment in Unit 61580; the unit has engineers specializing in “computer network defense and attack,” according to the Project 2049 Institute, a nongovernmental organization in Virginia that studies security and policy issues in Asia.

Members of Unit 61398, the bureau mentioned by Mandiant, have written several papers on hacking and cybersecurity with professors at Shanghai Jiaotong University, which has a prominent information security department. Across China, the universities labeled jiaotong — meaning communications — are taking the lead in building such departments. The military recruits at the universities and runs its own training center, the P.L.A. Information Engineering University, in the city of Zhengzhou.

But cybersecurity experts here say the schools often churn out students who know theory but lack practical skills. That could explain why many Chinese hacking attacks that have been discovered do not appear very sophisticated. American cybersecurity experts say attacks from Chinese groups often occur only from 9 to 5 Beijing time. And unlike, say, the Russians, Chinese hackers do not tend to cloak their movements, said Darien Kindlund, manager of the threat intelligence group for FireEye, a cybersecurity firm in Milpitas, Calif.

“They’re using the least amount of sophistication necessary to accomplish their mission,” Mr. Kindlund said. “They have a lot of manpower available, but not necessarily a lot of intelligent manpower to conduct these operations stealthily.”