A Microsoft file hosting and synchronization service.
I was fortunate to have almost all my data in OneDrive cloud, albeit with thousands of duplicates. (I wonder who had the bright idea of adding suffix " - Copy"? It's a term you can't search for even if you use file: so the dups have to be hand zapped.)
I agree very much re their deletion of our data. If anyone else was caught deleting data from a machine, they'd be arrested!
Microsoft seem to insist that you go straight to the cloud for working files. That's okay if you work for Microsoft and a dirty great data pipe, but many mere mortals have slower data speeds. I hate it that you can't exclude the OneDrive folder from windows seearches. If I type in the name of a file in my local drive, it always suggests the copy on OneDrive. It's very annoying.
My message is .. stay calm! It's not worth the ulcer. (I know, I've had them.)