Taiwan's main opposition Democratic Progressive Party said yesterday that its headquarters had been targeted for six months by hackers working for Beijing.
Alex Huang, director of the DPP's policy research committee, said the attacks were linked to Taiwan's presidential and legislative elections, which are scheduled for January.
However, Mr Huang said that the DPP presidential candidate Tsai Ing-wen's email had not been affected. Ms Tsai is standing against President Ma Ying-jeou.
A report by a computer security firm found one source of the attacks was the bureau of China's official Xinhua News Agency in Kuala Lumpur, Malaysia.
"Most of our party officials have had their emails hacked into and we have lost sensitive documents concerning campaign schedules and promotional material," Mr Huang said. "Some of the computers have been planted with Trojans."
Taiwan and China split after the civil war in 1949, when Chiang Kai-shek fled to the island with his Kuomintang (KMT) Nationalists. Beijing continues to claim Taiwan as Chinese territory.