Public Class Form1
    Declare Function WindowFromPoint Lib "user32" (ByVal xyPoint As Point) As _
      IntPtr
 
    Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As Object, ByVal e _
      As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        Dim handle As IntPtr = WindowFromPoint(New Point( _
        Control.MousePosition.X, Control.MousePosition.Y))
        Me.Text = handle.ToString
    End Sub
End Class