The flaw is unusually widespread, affecting all versions of DirectX from version 5.2 to the current 9.0a running on all versions of Windows from Windows 98 through the new Windows Server 2003, according to the Microsoft bulletin.

The flaw, which received Microsoft's highest severity rating, involves the way DirectX handles MIDI music files. A malformed MIDI file could overrun the buffer in DirectX, at which point extra software embedded in the file would be executed.
Exploiting the flaw would entail the creation of a maliciously malformed MIDI file, which vulnerable Windows users would have to be tricked into running, either through e-mail or a Web page.

Read more: CNet News.