The only way to be absolutely sure would be to save these files to a removable media such as a CD-R, or a floppy. Then go back and erase the original files and clear out the cookies in their sub folders. This will stop someone who is not an expert from seeing them. It sounds like your method should be okay, unless someone gets curious and looks at your folders.

A standard back round check does not usually involve tracking all of your computer usage, not in the U.S. anyway (at least for now ).
Barton.