Diskimage.Sparsebundle has corrupted file. .DS_Store data appeared in Excel spreadsheet

• This is a classic case of data corruption at the file level. The data at the start of the Excel file has been over written by data that should be in the .DS_Store file.

This opendiff listing shows a side by side comparison of .DS_Store file and the broken Excel file. Note the .DS_Store data at the start of the Excel Spreadsheet ....

Note the Bud1 text which is the DS_Store fingerprint.

• It's very hard to spot when such data corruption has occurred as there is no external visible marker (except in this case the unix file type). The problem only becomes apparent when the Excel file is opened.

• Some file types are identified by the dot3 or four letters on the end others are identified by data markers within the file. Excel appears to use a combination of both to identify whether a file has a password encryption or not. In this case, corrupted contents of a spreadsheet prevented from being opened.

• I logged this as a support case with Apple but unless I can recreate the issue easily - not much chance it will progress being that it occurred on previous machine.

• AAAARGH lucky I have backups and know how to use them.

• Read more about .DS_Store files and some of the problems they cause here.  

Working encrypted spreadsheet 
BBComp % strings 2024-0402-082024_BBCFirst/DoshNsav_pivZ.xlsx| head
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<encryption xmlns="http://schemas.microsoft.com/office/2006/encryption" xmlns:p="http://schemas.microsoft.com/office/2006/keyEncryptor/password" xmlns:c="http://schemas.microsoft.com/office/2006/keyEncryptor/certificate"><keyData saltSize="16" blockSize="16" keyBits="128" hashSize="20" cipherAlgorithm="AES" cipherChaining="ChainingModeCBC" hashAlgorithm="SHA1" saltValue="cfDF3XFob
T&,9
"&Z#
ae+B
'd/#
[)ps
Yjx5<
Y!
 b
1Bi2

For one of the broken file: 

BBComp % strings 2024-0402-082024_BBCFirst/DoshNsav_Trackers_piv.xlsx| head 
Bud1
nIlocblob
gIlocblob
smodDdutc
sdsclbool
slsvCblob
Bbplist00
WXWY
  [XiconSize_
showIconPreview_
calculateAllSizesWcolumns_

Looks like some damage here to the disk image which was made a long time ago.

Full write up here on Sonoma 14.4 with latest versions of Excel.

Please add to this comment if you have seen examples of file corruption during normal use of DiskImage Sparsebundles.

What's needed now is a script that reliably recreates the issue.