We have most of our documents backed up and syncing in MS Sharepoint. That has worked very well for us. However, I just noticed an old folder I created on the C: drive at the time of setting all this up -- a duplicate of the all the files in Sharepoint.
In this folder, named "Secret Backup" are hundreds of doc, docx, and xls files, mostly donor thank you letters from 10 years ago. All of the MS Office files have the same dates as those that are backing up in sharepoint, but the file size is 5-10kb smaller. PDFs and JPGs are identical in both locations (no file size difference).
No human is bothering to open up those old files. I'm not uber-savvy about viruses, but is it possible that some other computer that syncs the Sharepoint folder has a virus on it, and some code has been added to all the syncing files?
Avast doesn't identify any problems with either the short or the longer files, and Sharepoint version history shows only one version of the files.