I've been sent to an emergency before, not a client, but contacted us for emergency help as we were a close IT firm, and they had their backups stored on a local NAS, that replicated to an offsite NAS.
But both sites were flat networks, security didn't really exist in any of the setup, the domain administrator account was used for access to the NAS shares for example, and that's the same account the backup software used to access everything.
Once the hackers got hold of that password, they deleted everything they could from the backups.
What was interesting though and the reason I bring it up here, I didn't want to name Synology, but it's worth putting out and apparently, this is fixed in newer firmware releases, but on the firmware this company was on, the hackers had logged into the NAS's with some engineering account and completely hard reset both NAS's.
That didn't delete the data on the drives, I was able to re-setup the NAS's, it discovered the existing RAID and put itself back together again, the hackers did a poor job of deleting the backups, they logged into the software (Veeam) and deleted the backup jobs etc... but didn't check Veeam had actually deleted the data, which it hadn't luckily for me. Then I just restored everything to a new Azure environment that was actually locked down.