China has hacked into the computers of Angela Merkel’s Chancellery and three other German ministries in an extraordinary economic espionage operation that threatens to blight the German leader’s already delicate trip to Beijing this week.

The claims, made in a detailed investigation by Der Spiegel magazine, were denied strenuously by the Chinese authorities yesterday, but there was no mistaking German anger. “If true, it is unacceptable,” Ralf Stegner, a senior Social Democrat, said. “China is a competitor as well as a trading partner. Mrs Merkel has to get to the bottom of the affair on her China trip.”

Mrs Merkel arrived in China last night with senior business executives determined to put concern about product piracy high on the agenda. “We are pursuing the issue of protection of intellectual property very strongly with China,” said Mrs Merkel, who refused to discuss the espionage claims.

Der Spiegel, quoting senior officials from the German equivalent of Special Branch, said that the hacking operation was discovered in May. Computers in the Chancellery, the Foreign, Economics and Research ministries had been targeted. The Federal Office for the Protection of the Constitution (BfV) conducted a comprehensive search of government IT installations and prevented a further 160 giga-bytes of information being transferred to China. Commentators described it as “the biggest digital defence ever mounted by the German state”.

The information was being siphoned off almost daily by hackers in Lanzhou, northern China, in Canton province and in Beijing. The scale and the nature of the data being stolen suggest, the investigators say, that the operation must have been steered by the State and, in particular, the People’s Liberation Army.

“Does this Chinese man now know all our government secrets?” an outraged Bild am Sonntagasked yesterday next to a large photograph of General Cao Gangchuan, the Chinese Defence Minister. The content of the stolen data has naturally not been disclosed. “It can only have been interesting for state institutions,” said a confidential report by the BfV leaked to Der Spiegel. “So we must assume that the Chinese State is involved in the electronic attacks.”

Investigators caution that businessmen should not leave their laptop computers in hotel rooms while at official functions because of the risk of data theft. And all information transferred from China to German corporate headquarters should be encoded. “I have become really worried about Chinese espionage in the technology area,” says Hartmut Schauerte, parliamentary minister in the Economics Ministry and a China specialist.

The suspicions are now so deep that the motives of Chinese researchers at German universities are being questioned. Yesterday the Chinese Embassy in Berlin described the accusation of state-steered hacking as “irresponsible speculation without a shred of evidence”.

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