Some versions of Microsoft's Windows operating system are vulnerable to attack from hackers exploiting a flaw in the software that could allow them to remotely take control of a personal computer.
The software giant warned of the problem in a special alert. It said it has yet to develop software to plug the hole in Windows or to figure out a workaround to the problem.
Microsoft said it is not aware of any attacks that tried to use the vulnerability, which involves the way Windows renders graphics on versions of Windows XP, Windows Vista, Windows Server 2003 and Windows Server 2008.
The problem does not affect Microsoft's most-recent PC operating system, Windows 7, and its newest operating system for servers, Windows Server 2008 R2.