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.

Does 9.0b fix that?

I don't know (have not checked) but I would imagine that that would explain 9.0b 's sudden arrival I have certainly downloaded and installed 9.0b as soon as I read about it here.

Another bug :eek:

Do they ever check they're software for this kind of stuff?? Its posted all the time

I guess it's safe to say that we should all avoid MIDIs for a short while until the problem is completely solved.

The scary thing is that we can trail off to a site that has embedded MIDI inside the HTML and we could be attacked by it.

Yes, DirectX 9.0b fixes this.