Taiwan got another spy shock recently when they arrested two men who were spying for China. The shock part came from the fact that one of the men, Lo Chi Cheng was an army colonel. The other was an unnamed Taiwanese businessman who had business in China and spied on China. Then came another shock. The other guy was really a double agent, who had recruited the colonel, who obtained classified information that was then delivered to China. The government insisted that the data lost was inconsequential, but then that's what is normally said in such situations. No other details were released.
China and Taiwan have been spying on each other for over 60 years. The espionage activity has greatly increased as the Chinese economy shifted to a market model in the last three decades, and Taiwan was allowed to invest in China. The Taiwanese thought this would be an intelligence gold mine, but it's hard to say for whom.
Four years ago, a confident China released a lot of information about how Taiwan recruits spies inside China. Taiwan uses the Internet, trolling chat rooms and bulletin boards, as well as emailing likely candidates, and even using online ads. Actually, the Taiwanese are simply doing openly, what the Chinese have been doing clandestinely, for decades. The Taiwanese were not asking for anything that one would think of as state secrets. Mainly, they asked for unclassified magazines and documents that, because of their specialized nature, are only going to be found in China.
However, in China, which is still basically a communist dictatorship, and bureaucrats can declare as espionage anything they want, you can have the secret police on your case for anything. Chinese bureaucrats do just that, and the accused ends up in prison, or worse. So, while China feels free to collect unclassified material in foreign countries, don't try and do it in China.
Apparently, the Chinese ordered the media to publicize this nefarious Taiwanese plot in order to discourage Chinese from getting involved. Then again, it will also make more Chinese aware of a new way to make money easily, if a bit dangerously. Meanwhile, every few months, spies are arrested on both sides of the Taiwan Straits, indicating that Chinese and Taiwanese spies are hard at work, despite the dangers (long prison terms and, in China, execution for the worst offenders.)
All this espionage is mainly a business, with cash, or favors, exchanged for valuable data. Some spies do it out of altruism (patriotism, anti-communism, whatever), but for most it's just business, a very dangerous business.