Somebody discovered a way to sneak remotely into Windows computers under some circumstances (only in the laboratory so far, but some smart person will figure it out in the real world eventually). Microsoft has a patch that eliminates the problem, and it’s trying so hard to be sensitive to security issues that a Microsoft guy took the lead in announcing that this was serious and awful and everybody should upgrade immediately.
This is an issue for Windows XP, Windows ME, and Windows 98 (sometimes). The patch will turn up on the Windows Update site eventually, but it doesn’t seem to be there yet today. Even without doing anything, if you’re running Windows XP you should see a balloon in the next few days down by the clock that says an update has been automatically downloaded and is ready to be installed. One click and it’s done. But I recommend that you take the initiative on this one and click here to go to the Microsoft security bulletin where you can download the update today.