To decline the test updates, users must set the Windows Update control panel to something other than the recommended "Install updates automatically," then right-click each fake update that appears and select "Hide update" to delete it from the list.

Microsoft has already released one legitimate update for Windows 7 RC. On Thursday, the company that had slipped through testing. If left unfixed, the bug can cripple applications or block them installing properly, Microsoft said in a support document.

The fix was delivered through Windows Update starting Thursday. Computers running Windows 7 RC that have Automatic Updates set download and install patches should have already received and installed the bug fix.

Microsoft publicly last week, several days after it posted the preview on MSDN and TechNet, the company's developer and professional IT subscription services.