It's not dropbox I'm worried about, so much as the fact that a system that has the ability to make public any file at the owners direction, could be potentially

It's not dropbox I'm worried about, so much as the fact that a system that has the ability to make public any file at the owners direction, could be potentially exploited to make public any file without the owners direction. Are non-public files now accessible to third parties who have the correct url? Is there code that maps encoded url's to every file in my dropbox? If so, this is a security vulnerability that is not present currently.