| ® | 236 | HOW AMERICA LOST ITS SECRETS on the campuses of its universities. Its hierarchy is also obscure. Few traces have been uncovered of any conventional espionage net- works in the United States, and no major Chinese spy has ever been arrested. Part of the reason that Chinese espionage has proved so elu- sive to the eyes of Western counterintelligence is that, unlike Russia, it did not ordinarily rely on intelligence officers in its embassies to recruit penetration agents to steal secrets. It did not even have an embassy in the United States during most of the Cold War. Instead, its services specialize in mosaics of intelligence assembled from a wide variety of sources, including nonclassified documents, return- ing graduate students, scientific conferences, exchanges with allies, and a vast operation of hacking into computers, or cyber espionage. Such espionage is indeed a vast enterprise in China. Graduating over 150,000 computer science engineers in the 1990s, it had no shortage of personnel. It had also developed the cyber tool kit to gain access to the computer networks of U.S. government contractors and consultants in the private sector and government agencies, planting “sleeper” bugs in networked computers. Like human sleeper agents, © these hidden programs can be activated when needed for operational re) purposes. Chinese controllers can often retrieve e-mails and docu- ments and can turn on the cameras and microphones of personal computers, tablets, and smart phones. By 2007, Paul Strassmann, a top U.S. defense expert on cyber espionage, reported that China had inserted “zombie” programs in some 700,000 computers in the United States, which could be used to mount cyber attacks to retrieve e-mails from other computers. The Chinese service also reportedly penetrated companies that provide Internet services, including Google, Yahoo!, Symantec, and Adobe, which allowed it to track e-mails and enclosures of individuals. With such an invisible army of