A demonstration of the problem has been posted to the Web by the programmer who discovered it, Fabio Ciucci of Italy.
Ciucci's demonstration identifies the bug as a problem with Microsoft's Internet Explorer browser, but it actually affects any implementation of the DirectDraw classes, according to Microsoft.
Those classes can be found in IE 4 and above; in Windows 95, 98, and NT 4; and in Microsoft's Java software development kit.
A class describes a set of Java code that produces a certain effect or functionality, such as a button on a screen or the act of opening a dialog box or window.
At issue with the bug is graphics functionality. DirectDraw, the less popular cousin of Microsoft's DirectX technology, cannot understand a certain command that it ought to be able to execute. When posed to it, the command causes the system to freeze. The only way to recover is to reboot the computer, causing unsaved data to be lost.
"This is a denial-of-service problem in that it prevents you from using the system," said Microsoft product manager for platform marketing Joe Herman. "[Ciucci's] applet is hanging the system, and it's a bug that we need to correct."
Herman described the bug as serious but obscure.
"The fact is that there aren't many applets that are built with DirectDraw, so not a lot of people are going to stumble on this. These classes have been around for three-and-a-half years, and we haven't run across this yet."
Herman did not know when Microsoft would issue a patch.