Like the ghost of antitrust past, China this week announced that Internet Explorer and Windows Media Player are the targets of its recently launched antitrust investigation against Microsoft. The software giant has faced similar probes in the past—the distant past. Why is China dredging up this old and presumably superfluous issue now?

Part of the answer may lie in Internet usage patterns that are somewhat unique to China. While the country, like the rest of the world, is of course racing to embrace mobile computing devices such as smart phones and tablets, Internet access there still occurs primarily through PCs. So the country's exposure to outside information—which the authoritative government there routinely tries to block—occurs mostly through Windows. More specifically, it occurs through Windows applications like the Internet Explorer web browser and Windows Media Player.

Of course, Microsoft got into trouble for bundling IE and Media Player in 2001 in the United States and 2004 in the EU, respectively. Since then, mobile computing trends have relegated Windows and PCs to a minority share of the worldwide personal computing market. China is simply on the trailing edge of that change.

On Tuesday morning, Zhang Mao, the head of China's State Administration for Industry and Commerce (SAIC), held a press briefing detailing the charges. He added that Microsoft has not been "transparent" with information about how it sells Windows and Office, but that the firm has thus far willingly cooperated with the investigation.

Mao said that his agency has been looking at Microsoft's business practices since June 2013 because of application bundling, compatibility, and "document authentication" issues in Windows. The SAIC's formal investigation of Microsoft is just one of several such investigations of domestic and foreign companies launched this year that span the software, telecommunications, insurance, tourism, tobacco, and utilities sectors.

Microsoft has issued no comment about the charges.