All files in a subdirectory of OneDrive are unable to be opened and the programs report that they are corrupt or file type is not recognized. When I look at them using a raw editor, I see the following in the header of all the files:
SafeGuard FileEncryption
Copyright 1998-2012 Sophos Group. All rights reserved. SafeGuard is a registered trademark of Sophos G
However, I have never encrypted the files.