The Chinese State Administration for Industry and Commerce (SAIC) has confirmed that it is looking into Microsoft's business practices and did raid its local premises as part of a competition study.
The SAIC has released a statement, which reveals that 100 law enforcement agents were sent to four Microsoft offices on "antitrust raids" and left with a mix of documents, interview write-ups and equipment.
"SAIC believes that Microsoft can not be eliminated through early verification of anti-competitive behavior above suspicion," it said. "By law, the State Administration for Microsoft's alleged monopolistic behavior has been a criminal investigation."
The note said that the SAIC raids included interviews with senior staffers, including marketing and legal teams, and saw the confiscation of hardware and documents. It added that the investigation continues.
Microsoft confirmed that the Chinese authorities have raided some of its premises, earlier this week, but did not dwell on the details. "We aim to build products that deliver the features, security and reliability customers expect and we're happy to answer the government's questions," it said.
Microsoft could be referring to concerns about the integrity of its hardware and software, but it would not disclose any further details about the raid.
The raids come at a time of tense relations between China and the US, particularly US tech companies. Microsoft has had to deal with its own Chinese controversies and in February it was forced to deny that it was censoring Bing searches on demand.
"China's position on the issue of network security is consistent and clear," it said in a statement. "China is a staunch defender of network security. The Chinese government and the army never engaged in any theft of trade secrets by network activity. From the WikiLeaks to the Snowden incident, the US hypocrisy and double standards on the issue of network security has long been obvious."
We have already seen Cisco seeking to distance itself from suggestions that it installs backdoors in its own exported hardware, and it is possible that Microsoft has faced similar allegations.
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