Hidden data in Excel files

Where spreadsheets hide things

Hidden is a display setting. The data stays in the file.

• Hidden worksheets, including "very hidden" ones that do not appear in the unhide menu at all
• Hidden rows and columns, which are one right-click from visible
• Cell comments and notes, each with an author name
• Document properties — author, company, last editor
• Column headings that reveal what the data is even when the cells are gone: "Salary", "DOB", "National Insurance"
• Defined names and formulas pointing at data that was supposedly removed

Why we will not delete a hidden sheet for you

This is a deliberate design decision and it is worth explaining, because it is the one place our cleaner stops and asks.

Deleting a hidden worksheet can break the workbook. Formulas elsewhere may reference it, and removing it turns those cells into reference errors — a working spreadsheet becomes a broken one, and the person may not notice until someone else opens it.

So hidden sheets are reported rather than removed. Properties and comments are cleaned automatically; the structural decision stays with the person who understands the workbook.

The heading problem

Sometimes the sensitive thing is not a value but a label. A column headed "Disciplinary outcome" tells you what the file is about even if every cell under it is blank, and a sheet of employee IDs next to a column headed "Grievance" is disclosive on its own.

Detection therefore looks at headings as well as cell contents.

What to do today

Until Excel support is switched on here: unhide everything before sending — select all rows and columns and unhide, then right-click a sheet tab and check for hidden sheets. If a sheet does not appear there, it may be "very hidden" and only visible in the VBA editor. Then delete what should not travel, rather than hiding it.

Better still, copy the cells you actually want into a new workbook. A fresh file carries none of the old one’s history.

Questions