The MSS is the primary Chinese HUMINT collection organization, although the MID is also involved in HUMINT collection. The MID is primarily involved in the overt collection of technical information through visits to trade shows, military exchange programs, and through the military attache program. The MSS is responsible for both overt and clandestine collection. It uses students, diplomats, businessmen, and scientists in its attempts to gain information. China has been extremely aggressive in its HUMINT collection activities in the United States. The PRC has more than 2,600 diplomatic and commercial officials in the United States. A substantial percentage of these personnel are actively involved in collecting intelligence. More than 40,000 students from the PRC also attend schools in the United States, and many of these students have been tasked to collect information by the Chinese government. In addition to these personnel, over 25,000 Chinese visit the United States each year as members of official delegations, and an additional 20,000 Chinese emigrate to the United States annually.The MSS has been able to obtain high- and mid-level technologies not cleared for export to the PRC through its activities. It has used three principal means to obtain such technology: first, recruiting agents in China and sending them abroad to acquire technology; second, acquiring American firms that produce a desired technology; and third, the use of MSS operated front companies in Hong Kong. The Chinese have used a number of different methods to gather HUMINT. They have used pressure to gain information from the Chinese immigrant community, especially on those Chinese that have access to high technology or military data. The MSS has also encouraged Chinese students to remain in the United States as long-term penetration agents. MSS personnel have acted as intelligence collectors using cover as NCNA reporters, trade office representatives, and accredited diplomats. Scientific exchange programs have proven to be extremely useful means for the Chinese to gather information. The FBI has stated that virtually all Chinese allowed to leave the PRC for the United States are given some type of collection requirement to fulfill. Although the bulk of Chinese operations are not sophisticated operations, the large number of ongoing Chinese operations greatly increases the difficulty of countering their espionage activities. In recent years, the Chinese have been the subject of approximately half of all cases initiated by U.S. law enforcement agencies concerning the illegal diversion of technology from the United States.