Beijing dismissed both reports as without foundation. But Taiwan experts say that hacking methods such as those outlined in the Mandiant report are the same kinds of security breaches that they had seen several years earlier.
Regarded by China as a renegade province it must recover, by force if necessary, it is easy to see why Taiwan might be an ideal target for Chinese hackers: it is close to the mainland, Mandarin-speaking and boasts advanced internet infrastructure.
This cyberwar playing out across the narrow Taiwan Strait first came to public attention in 2003, when a Taiwanese police agency realized hackers had stolen personal data, including household registration information, from its computer system.
These attacks differed from traditional hacking attempts - where many casual hackers attempt to disrupt their targets' systems, these hackers went in stealthily, with the intention to plunder rather than destroy.
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"Back then it was very rare to see these kinds of social network attacks," said hacking specialist Jeremy Chiu, a contract instructor in IT for Taiwan's intelligence agencies. "They were very, very well organised."
Other indicators, including the ease with which the hackers penetrated an email system written entirely in Chinese, painted a picture of the culprits as a large, coordinated group of mainland Chinese hackers.
"One thing that indicates government support for these attacks is just the sheer volume - how many agencies are being attacked on a daily basis," said Benson Wu, postdoctoral researcher in information technology at Taiwanese think-tank Academia Sinica and co-founder of Xecure Lab, which focuses on responding to advanced persistent threats.
Interviewed at his downtown Taipei office, Wu's set-up fits the classic hacker image: dimly-lit, strewn with wires and humming with computers.
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On a projector screen he displayed a list of emails, written in Chinese, with subject headings like "meeting notes", "dinner attendance" and "questionnaire".
"These are all hacking attempts," Wu explained. Once the documents have been opened, they plant a backdoor allowing the hacker virtually unfettered access to the network.
One such "spearphishing" attack was reportedly used on the White House in October. A Taiwan expert in cyberespionage interviewed by Reuters estimated that thousands of Taiwanese high-level government employees receive as many as 20 to 30 of these emails a month.
"We've been following these Chinese hackers for so long, we can track their daily work schedule," said the expert, who asked not to be identified.