Answer:
A shared user with Administrative or elevated privileges can see everything you type (including back spaces) by using an application called a key stroke logger. Usually these apps run secretly well hidden from users. You have to know who the Application vendor is in order to know the key combination necessary to pull up the application. It will not be found in the application menu (obviously). Only way to avoid this is to use only your trusted computer where nobody else would know the administrative password. This is why all should be careful when using PC's like at libraries & books stores, public kiosk, and especially the Apple stores...