See http://www.fas.org/sgp/crs/nuke/RL30143.pdf including Summary from Congression Research Service report - which reads in part :
"This CRS Report discusses China’s suspected acquisition of U.S. nuclear
weapon secrets, including that on the W88, the newest U.S. nuclear warhead. This
serious controversy became public in early 1999 and raised policy issues about
whether U.S. security was further threatened by China’s suspected use of U.S.
nuclear weapon secrets in its development of nuclear forces, as well as whether the
Administration’s response to the security problems was effective or mishandled and
whether it fairly used or abused its investigative and prosecuting authority. The
Clinton Administration acknowledged that improved security was needed at the
weapons labs but said that it took actions in response to indications in 1995 that
China may have obtained U.S. nuclear weapon secrets. Critics in Congress and
elsewhere argued that the Administration was slow to respond to security concerns,
mishandled the too narrow investigation, downplayed information potentiallyunfavorable to China and the labs, and failed to notify Congress fully...."