Do you think that protect your Excel worksheet with password is safe? You are wrong!

Starting with Office 2007, Excel files use the Open Office XML File Format.
It’s an open standard, really well documented:

Each Excel workbook contains of a bunch of folders and XML files.
XML stand for Extented Markup Language: it works with opening and closing tags, similar to HTML.
Worksheet protection is defined in a specific tag into XML file:if you remove this tag, you can remove the protection.

Now let's see how remove protection from worksheets (please note that this method works with the worksheet password and not with workbook password):

  1. Rename the XLSX file as ZIP
  2. Extract the ZIP archive
  3.  Into the extracted archive (in xl -> worksheets  folder) you can find some XML files that contains data and metadata of the worksheets.
    Open every file with your favorite texteditor, search the XML tag named sheetProtection and remove the entire tag.
    Save the files.
  4. Compress the extracted files (with the same folder structure) in a new ZIP file
  5. Rename the ZIP file in XLSX.

Well, do you have a more simple method?

Yep! Download and install Libreoffice, open the file with Libreoffice Calc and unselect the option "Protect Sheet" under "Tools" menù.

Thats All Folks!