Set your QNAP to require authentication for the SMB share (not open), and use StorageCraft SPX (for just one example, I do recommend it) which can authenticate to that share outside of Windows authentication. This way, only SPX has the authenticated connection, not Windows itself, not any user or system profile in Windows; so if that Windows gets infected, ...
I've been using this free software for a decade now and it's excellent. Programmed by an individual in a "simple, basic" way, it requires minimal system resources and is extremely flexible, allowing scheduled backups of any group of subdirectories to any target subdirectories you want.
I eventually bought the ...
I use Duply (simple Duplicity) for my Linux server backups because:
it is incremental
the backup is encrypted
it is simpler than Duplicity
As mentioned here, it can be configured on Ubuntu to backup to DropBox (I never tried myself).
Here is a list of protocols mentioned as theoretically supported on the duplicity page:
This was possible by combining tools in the AWS ecosphere.
Backup from the lab PCs to an Amazon S3 bucket is done via an AWS Storage (File) Gateway. This also provides file-level access to the bucket. A hardware appliance can even be installed in the lab for terabytes of cache.
Versioning of the S3 bucket is done by periodic backups to Amazon Glacier.