It is unclear how the ban will impact Microsoft's China business but the sudden announcement was an obvious gesture that foreign-made software is not welcomed in government offices.

Microsoft described the new regulation as "extremely unexpected" on Tuesday afternoon.

"We have been working proactively with the Central Government Procurement Center and other government agencies through the evaluation process to make sure that our products and services meet all government requirements," the world's largest software company told China Daily in an e-mailed statement.

"We are also working closely with relevant departments to evaluate Windows 8 for government purchase in the future."

Industry regulators have been openly calling for made-in-China systems for many years.The latest public support came from the Ministry of Industry and Information Technology Spokesman Zhangfeng. He pledged in mid-May that the ministry will put "increasing focus" in helping Chinese companies develop Linux-based OS in a bid to lower safety risks.

"The issue of security of foreign software products is not an unnecessary self-inflicted one," said Liu Yufeng, executive deputy general manager of Guangzhou-based ZWCAD Software Co, which develops computer-aided design and manufacturing products.

"Software backdoor may pose risks to the government, national defense, the military industry and other businesses," Liu said.

Impact to tech stocks

Although the government has not spelled out the exact reason behind the ban, analysts speculate high cost and compatibility are two primary causes. The retail price of Windows 8 in China is 888 yuan ($142) and its predecessor Windows 7 costs about 400 yuan ($64.4).

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