Ukraine recently convicted a Russian, Aleksandr Yermakov, of spying for China, and sentenced him to six years in prison. Yermakov was hired by China to steal details about the construction and operation of NITKA (the Naval Aviation Testing and Training Complex, built during the Cold War for Soviet carrier aviators). Three years ago, Chinese officials visited Ukraine and inspected these naval aviation training facilities. Ukraine wanted to use those facilities to establish an international center for training carrier aviators, and hoped to attract the Chinese as customers. But the Chinese were apparently just taking notes. Ukraine was aware of the fact that the Chinese steal technology, but, as far as carrier pilot training services went, there was no sale and not much to steal. The Ukrainians later discovered that the Chinese had drawn up a shopping list of NITKA stuff they wanted. China has bought some technology from Ukraine, but a limited amount of actual hardware. It's much cheaper to steal.
Last year, satellite photos revealed a new Chinese naval aviation training center on Hulu island (up the coast from Dalian in the Yellow Sea, where the former Russian/Ukrainian carrier Varyag is being refurbished as a training ship). This center was similar to the one in Ukraine, and the data that the Chinese spy was seeking was to make it more so. Meanwhile, Russia continues to use NITKA, providing Ukraine with at least one paying customer.
Aleksandr Yermakov had apparently been spying for China for most of the past decade, finding Russian military technology worth copying, and then helping the Chinese obtain samples, or technical details.