Computerworld reports that regulators in China today said that they made sudden appearances at several Microsoft offices on Monday to gather evidence for an antitrust probe.

In a note on its website, China's State Administration for Industry and Commerce (SAIC), one of several agencies tasked with enforcing antitrust laws, said that with the help of nearly 100 law enforcement officers, regulators made unannounced visits to four Microsoft offices in Beijing, Chengdu, Guangzhou and Shanghai.

SAIC said it was after information about how Windows and Microsoft Office are bundled, about Windows-Office compatibility, and about other unnamed concerns after fielding complaints since June 2013.

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