A lot of people suspect that the Chinese stole data from the F-35 project, which is probably true.
However, the Chinese are rapidly catching up to the west and Russia in technological expertise. The days when we could assume our technology would always be superior to theirs are pretty much gone.
Lets not forget, they have an active manned space program while the US is forced to bum rides from the Russians.
http://en.wikipedia.org/wiki/Shenzhou_9