OOXML is defective by design

I haven't tried this yet:

The entire article can be found here

Self exploding spreadsheets.

To reproduce the scenario :

• start Excel 2007 and create a new spreadsheet
• insert a value 10 in a cell
• insert a value 20 next to it
• select the two cells and click on the "sum" button to create a sum of the two cells
• save the spreadsheet (xlsx file)
• close it and unzip it

The corresponding XML in the main part is :

 
  10
 
 
  20
 
 
  SUM(C2:D2)
  30
 

Pretty simple XML. Now say we want to edit cell E2 and set a constant value of 40 in place of a formula. But instead of doing that with Excel 2007 interactively, we are going to do it manually :

• unzip the file
• grab a zip part known as xl/worksheets/sheet1.xml
• make the edit described below
• put the updated zip part back in the zip package
• zip it

The corresponding valid (and carefully changed) XML for setting the constant value of 40 in cell E2 is :

 
  10
 
 
  20
 
 
  40
 

Now open the file in Excel 2007.

The entire article can be found here