How do I check that a Windows QFE/patch has been installed from c#?

Question

What's the best way in c# to determine is a given QFE/patch has been installed?

Answer 1

Use WMI and inspect the Win32_QuickFixEngineering enumeration.

From TechNet:

strComputer = "."
Set objWMIService = GetObject("winmgmts:" _
    & "{impersonationLevel=impersonate}!\\" & strComputer & "\root\cimv2")
Set colQuickFixes = objWMIService.ExecQuery _
    ("Select * from Win32_QuickFixEngineering")
For Each objQuickFix in colQuickFixes
    Wscript.Echo "Computer: " & objQuickFix.CSName
    Wscript.Echo "Description: " & objQuickFix.Description
    Wscript.Echo "Hot Fix ID: " & objQuickFix.HotFixID
    Wscript.Echo "Installation Date: " & objQuickFix.InstallDate
    Wscript.Echo "Installed By: " & objQuickFix.InstalledBy
Next

The HotFixID is what you want to examine.

Here's the output on my system:

    Hot Fix ID: KB941569
    Description: Security Update for Windows XP (KB941569)
    Hot Fix ID: KB937143-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB937143)
    Hot Fix ID: KB938127-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB938127)
    Hot Fix ID: KB939653-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB939653)
    Hot Fix ID: KB942615-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB942615)
    Hot Fix ID: KB944533-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB944533)
    Hot Fix ID: KB947864-IE7
    Description: Hotfix for Windows Internet Explorer 7 (KB947864)
    Hot Fix ID: KB950759-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB950759)
    Hot Fix ID: KB953838-IE7
    Description: Security Update for Windows Internet Explorer 7 (KB953838)
    Hot Fix ID: MSCompPackV1
    Description: Microsoft Compression Client Pack 1.0 for Windows XP
    Hot Fix ID: KB873339
    Description: Windows XP Hotfix - KB873339
    Hot Fix ID: KB885835
    Description: Windows XP Hotfix - KB885835
    Hot Fix ID: KB885836
    Description: Windows XP Hotfix - KB885836
    Hot Fix ID: KB886185
    Description: Windows XP Hotfix - KB886185
    Hot Fix ID: KB887472
    Description: Windows XP Hotfix - KB887472
    Hot Fix ID: KB888302
    Description: Windows XP Hotfix - KB888302
    Hot Fix ID: KB890046
    Description: Security Update for Windows XP (KB890046)

Answer 2

The most reliable way is to determine which files are impacted by the QFE and use System.Diagnostics.FileVersionInfo.GetVersionInfo(path) on each file and compare the version numbers.

edit: I think there's a way to check the uninstall information in the registry as well, but if the QFE ever becomes part of a Service Pack or rollup package that might report false negatives