Microsoft is under investigation by Chinese regulatory authorities amid concerns about how it is distributing its Internet Explorer browser and Windows Media Player app, reports the Wall Street Journal.

Further Reading Microsoft China offices visited in apparent antitrust probe

This investigation explains in part the surprise visits made to Microsoft's China offices last month.

In a briefing, Zhang Mao, chief of China's State Administration for Industry and Commerce, announced that these products (as well as the sale of Office and Windows) were being examined. "Microsoft is suspected of incomplete disclosure of information related to Windows and Office software, as well as problems in distribution and sales of its media player and browser."

Microsoft has said that it will cooperate fully with the investigation.

Microsoft has, of course, been investigated for the bundling of Internet Explorer and Windows Media Player before. Both the EU and Korean competition regulators have taken issue with the inclusion of Media Player with Windows, resulting in the creation of N (for the EU) and K (for Korea) editions that omit the software. In both cases, it can be downloaded at no cost.

The inclusion of Internet Explorer similarly raised the ire of regulators, and EU Windows users are shown a browser selection screen so that they might pick another browser.

However, the Internet Explorer competition complaints were made at a time when Internet Explorer had upwards of 90 percent of the browser market. These days, it's closer to 50 percent on a global basis. China is, however, an outlier, with Microsoft's browser much more dominant there than elsewhere. Even Internet Explorer 6 remains significant in that market, with 12.5 percent of users sticking with the ancient browser.