Re: Excel security
Excel's read-only password protection is still garbage.
For .xls files (which we still use a lot of), it's fast and easy to break - create new workbook, protect with random password, run brute-forcing macro, wait 2 minutes - macro produces a usable password and an unlocked worksheet.
For .xlsx files, it's only slightly harder. Rename to .zip, unzip, open xl/worksheets/sheet_.xml, delete the tag sheetProtection, save, rezip, rename to .xlsx, and open. You can probably put it back after editing the file, to reprotect it with the same (unknown) password.
(Just tried these in Office 365 ProPlus.)