China’s State Administration for Industry and Commerce (SAIC) opened an anti-monopoly probe into Microsoft over problems arising from its Windows and Office software. This after a surprise raids of the company’s offices in the country.

An industry complaint in June 2013 alleged that Windows and Office are not fully open, resulting in compatibility, bundling and document verification issues.

On Monday, the regulator sent hundreds of staff to raid four Microsoft offices in Beijing, Shanghai, Guangzhou and Chengdu.

China is a huge market for Microsoft. However, in May, the Chinese government procurement agency began banning purchases of Windows 8 systems, taking Microsoft off guard. It is assumed that the ban came after Microsoft stopped support for Windows XP, a huge market share of the now abandoned operating system.