by saying that you only use the default username and no password then you have a world of posibilitys open to them. if your in win98 then theres not much in the way of restricting access to your computer if you are running a telent server...... win98 dosnt have a telent server (correct me if im wrong) so unless you put a server program on your machine then you probly dont have a telent port open. if the server that you have installed detects that windows is open up like that (no username and pasword) then it will probly not even prompt for it. if it dosnt detect that then itll still prompt but all they do is hit enter twice and there in.......

best advice, dont run a server if you dont know how to secure it. if you still have to then atleast use a password if not change usernames also.......