WASHINGTON  —  Microsoft Corp. on Thursday said that an investigation by Korea's antitrust watchdog could lead to the withdrawal of Windows from the country, or to delays in introducing new versions of the operating system there.

Microsoft's competitive practices have been under investigation by the Korean Fair Trade Commission (search), which is looking into the company's inclusion into Windows of streaming media and instant messenger technology.

The Redmond, Wash.-based software giant has faced legal and regulatory antitrust actions worldwide because of its decisions to include various services in its operating system.

Earlier this month, Microsoft agreed to settle an antitrust lawsuit with RealNetworks Inc. by paying up to $761 million in cash and services.

The Korean Fair Trade Commission said at the time that the RealNetworks settlement wouldn't have any effect on its investigation into Microsoft.

Seattle-based RealNetworks was among the companies that had filed complaints against Microsoft in Korea.

In its quarterly report filed Thursday with the Securities and Exchange Commission (search), Microsoft said the Korean commission could require the company to remove code or redesign Windows uniquely for the Korean market.

If that happened, "it might be necessary to withdraw Windows from the Korean market or delay offering new versions in Korea," the company said in the filing.

In morning trading Friday, Microsoft shares gained 49 cents, or 2 percent, to $25.34 on the Nasdaq Stock Market (search).