I wanted to post about this as after much research and searching, I did not find the answer on the internet and it shocked me !

Whilst reviewing one of my USB portable hard drives, I found a 24 Gb file on it simply called “Backup”.

No file extension. No obvious logs or anything to identify it.  Obviously it’s a backup from something. Is it 24 Gb of something I need ? It’s a big file and 24 Gb could be very important.

Viewing the header, and then looking for information online, nothing could identify it.




!BDN does not seem to relate to anything. Using a tool to extract ASCII strings from the file, resulted in no usable data.
No Mime headers, embedded properties or anything.
There is nothing else on the drive. Nothing to identify it and the date, is 6 months ago.

I worked out that !BDN is the header for a Microsoft Outlook OST file.

Using the Shellbags on my computer and working out what else I did on that day 6 months ago, I happened to run Scanpst.exe
This tool allows you to tell it where to place a backup of your PST or OST as it scans it for errors. Whatever you type into the browse box is the name of the file.
If you don’t attach the .Pst or .Ost extension to it and do as I did, types in “Backup” then that is the name of the file.

Now I know it is junk … deleting it.