1. If there is a dynamic textbox outside of the swf stage, is it possible a visitor to change it (even via a piece of script) or to view it?
2. If a username and password is stored in the swf on frame1, is it possible for a visitor to escape it or go pass it?
1. while viewing in the flash player, not yet.
2. maybe - right click on your swf and click play. see if the timeline advances. and they can certainly decompile your swf and check the username and password.