This story comes from a friend of a friend, so I cannot tell how much it true, but it another good example of showing some things are “obvious” only when you understand it.
I heard that some one’s office systems had been compromised by a ransomware attack, where their files had been encrypted and they money was demanded to decrypt them. The first whoops. While someone else was sorting the problem for the office, the person was pleased that he kept backups of all his key files, on a separate portable hard disk drive attached via a USB cable. The person realised that his backup files had been encrypted as well, so he was unable to restore his own backups of his key files. The second whoops. Looking back this was an obvious consequence of having the backups connected connected to the machine.
I would have expected that any decent backup package would make the files read only, but then if the ransomware was able to get into administrator mode, it would be able to change these “protected” files as well.
I think the only answer is to take backups off your machine – for example over a network, and hope the ransomware is smart enough not to corrupt files across a network. You could also backup your key files to a CD which is write once, and then becomes read only.
As I wrote this I remembered that I had been meaning to backup some family photographs and documents that only exist on my machine (and backups). I had sent a copy to my brother, but when he got a new machine he did not copy the files across!
I was also reminded of the University that diligently backed up the system every week. Which was fine until the building with the computer, and cupboard full of backups was destroyed in a fire.