The targeted attacks which I research are used by several groups, just about anywhere in the world. However, the techniques were probably seen executed in their most refined form by a number of Chinese groups, amongst others including the NCPH (Network Crack Program Hacker group) and HUC (Hunkers Union of China).

If these acronyms do not yet sound familiar, of if you're interesting in learning more on them, I can highly advise the book "The Dark Visitor" by Scott Henderson. The book, written by a Chinese linguist with experience in intelligence, offers some of the best insight currently available into Chinese hacker culture. In addition, he publishes a most excellent and regularly updated blog here. These are findings you do not want to miss out on.