Office updates files just read?

[pointertovoid]

Hello dear friends!

I regularly notice that (with Office 2003 Pro) XLS files are modified on my Internet machine, despite their modification date has not changed according to Windows, and their size neither.

Before I imagine some worm...

Can it be that Office writes in the file each time I open an XLS to read it but don't save the changes if any? And that Office restores the old modification date despite having altered the file's contents?

Thank you!

[submix8c]

What, exactly, is being Modified? Can you detect that?

edit - possible - BUT can't tell for sure UNLESS a "clean" XLS is placed into the affect machine and you "edit" (open/close) it and compare "binary" the differences.

quick "google" says SOME kinds of trojans exist, but you need to dfo above first to tell WHAT "may" have changed, otherwise...

Edited June 25, 2013 by submix8c

[Kelsenellenelvian]

Three letters...

NSA

[Tripredacus]

I had noticed, in the past, that some files have one of the 3 dates "changed" when you open a file but don't modify it at all. No real examples... But maybe you (op) can explain exactly what you are seeing.

[bphlpt]

But from what I understand from the OP, the file dates were NOT changed, but the content WAS? Very mysterious.

Cheers and Regards

[pointertovoid]

What I've seen:

- I make backups of my files between two computers, including XLS files, hence detect changes when synchronizing

- The file properties displayed by Window's Explorer remain the same, including the date of modification and the size

- But the synchronizing software tells that the files have changed

- The user's contents is the same

- When comparing both files with a text editor, hence in a big and not intelligible form, I see one tiny difference, like 2-4 bytes at one single location.

So before considering some kind of malware, I'd like to check more banal explanations.

One possibility would be that Excel stores a "last read date" within the file contents (and not at the containing folder as Windows does), updates it accordingly each time I read the file, but after writing the file with updated "last read date", restores the previous "date of modification" in the folder - something Window allows.

One reason why NSA-like explanations are not my first ones is that I notice this with XLS files only.

Edited June 26, 2013 by pointertovoid

[GrofLuigi]

I've noticed this as well, a long time ago. File and folder date isn't modified, few bytes inside the file are.

Excel 2003 does it, Excel 2010 doesn't.

GL

[dencorso]

I've noticed this as well, a long time ago. File and folder date isn't modified, few bytes inside the file are.

Excel 2003 does it, Excel 2010 doesn't.

Did you investigate it further? I mean... did you ascertain what those changes mean?

[GrofLuigi]

I've noticed this as well, a long time ago. File and folder date isn't modified, few bytes inside the file are.

Excel 2003 does it, Excel 2010 doesn't.

Did you investigate it further? I mean... did you ascertain what those changes mean?

I assumed it's something like "last access timestamp" or probably the counterpart of Word's "store random number to improve merge accuracy" which:

1. I never quite understood how it works

2. I read somewhere is the exact opposite of what it says, as regards to privacy

GL

[jaclaz]

- When comparing both files with a text editor, hence in a big and not intelligible form, I see one tiny difference, like 2-4 bytes at one single location.

Compare them in a HEX editor instead and post the offset at which the change occurs (it is likely to be a "fixed" address, but verify by checking more that on e "couple" of files).

Even easier , use FC (with the /B option) and post results:

http://ss64.com/nt/fc.html

jaclaz