Computer back-up qustion

You know jack s*it about how networking works, don't you?

Yes. The backup needs to be offline if it is to remain safe. You can get drive adaptors intended for forensic work that have a read only mode - physical switch so that write requests bounce off them. More expensive than normal kit and not as fast. I have one somewhere in a cupboard.

That copy should survive. Ideally you should cycle across three different physical sets of media in a grandfather, father, son regime. That way any single failure loses you at most a week/month's work.

Depending on how much you value your data and backups, it's worth having two backup disks and rotating them, and storing one off site, which covers you against backup disk failure, and fire etc.