Particularly interested in Windows XP, but all versions of Windows would be useful (if they differ).

EDIT: How does Windows/Windows Update know what to apply and what it has already done? Does it compare .dll/.exe versions or something else?


There is a log file located at %windir%\Windowsupdate.log which should have all information about updates performed on the system. Alternatively you could check the Add/Remove programs dialog and check off the Show Updates checkbox to see which ones are installed.

alt text

  • However, WindowsUpdate.log can be deleted. So can the %WINDIR%\Software Distribution\ directory which contains WU downloads. Add/Remove Progs doesn't seem to contain all updates (for example, the Malicious Software Removal Tool). – Umber Ferrule Mar 2 '10 at 17:18

When you click on Windows Update in XP, you'll see a link to view your update history.

alt text

  • Interesting - I never knew you could review this here. However, it doesn't necessarily list all WU. – Umber Ferrule Mar 2 '10 at 22:02

I've just come across the following Microsoft web page which sheds some light on the question: Command-line switches for Windows software update packages

Under the heading, Overview of the installation process, it states:

  • The [hotfix] installation program registers the software update under one of the following registry keys:
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Updates\<operating system>\<service pack level>\KB<nnnnnn>
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Hotfix\Q<nnnnnn>
    • HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\Hotfix\KB<nnnnnn>


  • Removal information for the software update is stored in a hidden folder named:
    • $NtUninstallQnnnnnn$ or $NtUninstallKBnnnnnn$ in %Systemroot%

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.