I run a daily backup that uses the file modified dates and file sizes to
determine whether to refresh an archived file. I tested this recently by
doing a binary compare between what should be an exact replica of the
directory, and the actual directory, to my suprise 5 out of 40 excel files
show a difference.

In all 5 files this difference is 6 bytes long, and for two of the files the
difference starts at file offset 0x46c. All files seem to open fine with
excel.

My first guess would be that this is a hash code windows writes to the
physical file once it is opened to handle the event of another excel instance
(or user) opening the same file. The problem is I can't seem to verify this.

Does anyone have any thoughts on what this difference might be? If not, can
you point me somewhere to find the answers I seek.

Thanks in advance,

Ryan