My condolences. Out of curiousity and caution, what version of Windows were you running? Was it up to date with patches? What was your virus scanner, if any?
These are valid questions, because if you either pay or somehow recover the files, you don’t want to e vulnerable to a re-occurrence.
I have to confess that our various systems are a patchwork of different versions of Windows operated on the different work stations, even back to Windows XP Pro. I’m not certain what the servers are running.