China has never been energetic at enforcing intellectual property laws. If a Chinese student came back with valuable technical information (obtained in a classroom, in a job, or simply while socializing), the data was often passed on to Chinese companies, or military organizations, that could use it. Since there were few individual Chinese bringing back a lot of data, or material (CDs full of technical data, or actual components or devices), it was difficult for the FBI to catch Chinese spies. There were thousands of them, and most were simply going back to China with secrets in their heads. How do you stop that?
The FBI has managed to crack the more ambitious of these spies, the ones caught red handed with actual objects. But most of the swarm moved back to China unhindered. Naturally, the Chinese pushed their system as far as they could. Why not? There was little risk. The Chinese offered large cash rewards for Chinese who could get particularly valuable stuff back to China. Chinese intelligence looked on these "purchases" as strictly commercial transactions. If the Chinese spies got caught, they were on their own. The Chinese involved knew the rules. If they were successful, they won favor with the government, or even made a pile of money, and the Chinese government was agreeable to whatever business deals these "patriotic" Chinese tried to put together back in China. This kind of clout is important in China, where a friend in the government is more valuable than in the United States.
China has been running a massive intelligence operation against the United States for over two decades. But they are starting to be victims of their own success, as the FBI round up more and more Chinese spies. China has been using a very clever, and effective technique to steal technology, and even military secrets, from the United States. Call it the swarming spies method. In the 1980s, China began to send thousands of students to American schools, and many more Chinese managers and technical experts began to visit as well. Chinese intelligence made sure they had a chat with many of these people before they left, and after they came back. The people going to America were asked to bring back anything that might help the motherland. Most of these people were not asked to actually act as spies, but simply to share, with Chinese government officials (who were not always identified as intelligence personnel) whatever information they obtained. Of course, it soon became open knowledge in China, and in American intelligence agencies, what was going on.
But more and more of these ambitious Chinese agents are getting caught, largely because the FBI has made the problem known to the American business and academic community. Chinese-Americans, in particular, have been very active in supplying tips to the FBI. The number of arrests the FBI has been making has been going up 20-30 percent a year for the past few years. The FBI has more work than they can handle.
The Chinese are feeling the heat, not that they are in any danger of being cut off from opportunities to steal American technology, though. But the Chinese system has reached its limits, and is being pushed back in some areas. It is thought that the Chinese are responding by trying to terrorize Chinese-Americans, at least those with family back in China, by threatening to make life uncomfortable for family members back in the old country if Chinese-Americans interfere with the spying, or any other Chinese government activities. The Chinese have been discreet with this. The last thing they want is a lot of stories of heavy handed pressure on Chinese-Americans. But arrests of Chinese-Americans back in China on business, or to visit family, sends a message. These arrests, and lesser forms of harassment, make it clear that there can be consequences. The Chinese deny any pressure tactics, but they are feeling the heat from the increased scrutiny of Chinese citizens in the United States, and the growing eagerness of Chinese-Americans to watch for this low level spying, and report it. The down side of the Chinese swarm system is that they are using amateur spies. Many dont even know they are spying, or don't think of themselves as spies. After all, the only thing they are doing is having a long talk with Chinese intelligence officials (usually with a technical expert in attendance), when they get back. Each of these conversations might yield a few useful bits of information. Putting a lot of these bits together and you get something useful, like how to build better jet engines, or nuclear weapons.
There are currently some 19,000 Chinese studying in American schools, and thousands more visiting for business purposes. Most want nothing to do with spying, but very few will refuse a request to have a chat with Chinese intelligence officers when they get home.