In Tips&Tricks Nr. 19, "Handling GuiXT activation in ABAP", you mention a Windows logon exit. What is this?

Please see either Microsoft Help (e.g. http://www.support.microsoft.com), or the examples available in Internet (search for "windows logon exit"). An example of a good explanation is http://computerperformance.co.uk/Logon/logon_script_assign.htm