Don't put things in the public Dropbox folder.
Dropbox corporation has by law to immediately hand over all files in any user account within 24 hours of a non-subpoena request from any of over a dozen Federal LEO Agencies.
With a subpoena, any LEO or prosecutor in the country can access all files uploaded to Dropbox.
This is the law of the land. It has been tested in court at least three times in the last 2 years.
The datacenter management industry is fretting over this law so much so they’ve spent millions of dollars lobbying Congress to change the law, because cloud computing becomes an unacceptable security risk to large corporations.