This is the second warning in just over a week of an ActiveX vulnerability that could allow attackers to take control of users' PCs through websites infected with malicious code.
The latest ActiveX hole is in Microsoft Office Web Components ActiveX controls.
The security risk affects Office XP, Office 2003, ISA Server 2004 and 2006, and Office Small Business Accounting 2006.
Users can prevent Web Components from running in IE using a manual workaround or Microsoft's automatic Fix-it tool.
Microsoft said it is working on a security update for all affected software.
This story was first published by Computer Weekly