How to determine whether a specific Windows Update package (KB*.msu) is installed using Inno Setup?

Question

I wonder how to determine whether a specific Windows Update package is installed in the target machine, lets say for example the Windows Update package with name KB2919355.

Exists a built-in feature to check that? If not, what would be the required code to determine it? Maybe messing with registry, or maybe a cleanest and/or secure way?

Pseudo-Code:

[Setup]
...

[Files]
Source: {app}\*; DestDir: {app}; Check: IsPackageInstalled('KB2919355')

[Code]
function IsPackageInstalled(packageName): Boolean;
  begin
    ...
    Result := ...;
  end;

Answer 1

function IsKBInstalled(KB: string): Boolean;
var
  WbemLocator: Variant;
  WbemServices: Variant;
  WQLQuery: string;
  WbemObjectSet: Variant;
begin
  WbemLocator := CreateOleObject('WbemScripting.SWbemLocator');
  WbemServices := WbemLocator.ConnectServer('', 'root\CIMV2');

  WQLQuery := 'select * from Win32_QuickFixEngineering where HotFixID = ''' + KB + '''';

  WbemObjectSet := WbemServices.ExecQuery(WQLQuery);
  Result := (not VarIsNull(WbemObjectSet)) and (WbemObjectSet.Count > 0);
end;

Use like:

if IsKBInstalled('KB2919355') then
begin
  Log('KB2919355 is installed');
end
  else 
begin
  Log('KB2919355 is not installed');
end;

---

Credits:

• The WMI query for updates:
  How can I query my system via command line to see if a KB patch is installed?
• Using WMI from Inno Setup:
  @TLama's answer to Inno Setup Pascal Script to search for running process.