My 2 cents on this:
A single vault is never going to protect you as a backup.
If a virus, or yourself would make changes to the files in your vault, Mylio woudl detect that and ask you if you want to apply them. In case you confirm they would get replicated to the other devices/vaults that are online or once they get online.
That said, in case of other computers with vaults on your network, the virus is very likely already on your other computers already anyway. So if your drives as vaults are connected they may already be impacted anyway even without Mylio replicating anything.
In case you make a human error and delete/change a file on one instance, once Mylio is active it will as i mention prompt you if these change shoudl be applied. This on condition that “Safe delete” is turned on (I believe thats the case by default anyway). in case safe delete is off, it will replicate all identified changes anyway (as instructed by you setting safe delete off)
A vault is very useful, but you need more then 1 in my opinion. As long as one of your vaults is disconnected and only synchronised once in a while, you would be safe.
That said, best woud be three
1 you are actively working on, 2nd one that’s synchronised actively or once in a while, to proof replication works. and a third one you keep offline and only connect if you are sure all changes are applied correctly and replication to the 2nd vault. Then connect the third vault and let it synchronise. Once synchronisation finished, disconnect it again for safety.
I have 4:
I’m paranoid in this but the vault function works amazing for me in Mylio. I have 4 vaults just to be sure and 1 is always away from the house just in case of fire. The offline/remote vault I switch every month or so. that way i cant loose too much of media. This way you are protected against human errors (at least many of them ) and many other types of issues.
This would also protect you from potential sw issues (be it Mylio or OS etc) as you always have an offline full copy of your media, or at least you won’t lose all, only since last sync.
In the past i did this with other sw and by backup sw to duplicate the drives etc. had cases that the backup “could not be read” and duplicating drives was in many cases a nightmare, especially if coudl need to keep multiple drives in sync from diffferent points you left off. Mylio keeps nicely track of this automatically.
So the vault works nice, and does protect you to some extend, depending how you use the function and how many you have. But you have to have multiple vaults to protect you from most issues. As explained I would say at least 3.
Hope this helps.