[X4U] Secure Empty Trash & Paranoia

[Jon Warms]

As I understand it, Secure Empty Trash writes over the disk area being deleted a sufficient number of times to prevent recovery of the deleted data, and to satisfy various security protocols.

Here's the first question: Does File>Save delete the old file in a secure way, or does it just delete the old file, then reuse part or all or none of that space as Finder sees fit, which could leave some or all of the old file deleted insecurely?

Let's say I have a password file (an Excel file, itself password protected). When I add, delete, or change an entry to the file and then save it, as I understand it, Finder first deletes the old file and then writes the new one. So the ghost of the old file may still be there for bad-guy recovery procedures.

For sure,  a more secure way would be to make my changes, then File>Save As a slightly different name. Then go to Finder and File>Move to Trash the old file and Secure Empty Trash. Question 2: Is this necessary to achieve a secure deletion of the old version of the file?

Hope I'm clear.

Jon