Nuclear espionage
In a 1999 report of the United States House of Representatives Select Committee on U.S. National Security and Military/Commercial Concerns with the People's Republic of China, chaired by Rep. Christopher Cox (called the Cox Report), it was revealed that U.S. security agencies thought there was nuclear espionage going on by the People's Republic of China (PRC) at American nuclear weapons design laboratories. The report said that China had "stolen classified information on all of the United States' most advanced thermonuclear warheads" since the 1970s, including the design of advanced warheads, the neutron bomb, and "weapons codes" which allow for computer simulations of nuclear testing (and allow China to advance their weapon development without doing its own tests). The United States apparently did not know of this until 1995.