Option Explicit
 
' zunächst die benötigten API-Deklarationen
Private Declare Function GetWindow Lib "user32" _
  (ByVal hwnd As Long, ByVal wCmd As Long) As Long
 
Private Declare Function GetClassName Lib "user32" _
  Alias "GetClassNameA" (ByVal hwnd As Long, _
  ByVal lpClassName As String, ByVal nMaxCount As Long) _
  As Long
 
Private Declare Function SendMessage Lib "user32" Alias _
  "SendMessageA" (ByVal hwnd As Long, ByVal wMsg As Long, _
  ByVal wParam As Long, lParam As Any) As Long
 
Const WM_SYSCOMMAND = &H112
Const SC_CLOSE = &HF060
Const LNULL = 0&
 
Const GW_HWNDFIRST = 0
Const GW_HWNDNEXT = 2
 
Private Sub Command1_Click()
  ' alle offenen IE-Fenster schließen
  Dim lRetVal As Long
  Dim sClassName As String
  Dim CurHWnd As Long
 
  CurHWnd = GetWindow(hwnd, GW_HWNDFIRST)
  Do While CurHWnd <> 0
    ' Klassennamen ermitteln
    sClassName = String$(256, " ")
    lRetVal = GetClassName(CurHWnd, sClassName, 255)
    sClassName = Left$(sClassName, InStr(sClassName, _
      Chr$(0)) - 1)
 
    If sClassName = "IEFrame" Then
      ' Explorer-Fenster gefunden - jetzt schließen
      lRetVal = SendMessage(CurHWnd, WM_SYSCOMMAND, _
        SC_CLOSE, LNULL)
    End If
 
    ' Handle des nächsten Fensters
    ' 0, wenn kein weiteres Fenster vorhanden
    CurHWnd = GetWindow(CurHWnd, GW_HWNDNEXT)
  Loop
End Sub