See the question and my original answer on StackOverflow

If you want to check if a Windows Edit Control has the ES_PASSWORD style, this is how to do it:

Public Shared Function HasPasswordStyle(ByVal hWnd As IntPtr) As Boolean
    Return ((GetWindowLong(hWnd, GWL_STYLE) And ES_PASSWORD) <> 0)
End Function

<DllImport("user32.dll")> _
Private Shared Function GetWindowLong(ByVal hWnd As IntPtr, ByVal nIndex As Integer) As Integer
End Function

Private Const ES_PASSWORD As Integer = 32
Private Const GWL_STYLE As Integer = -16