Troy Hunt does a great job of breaking down the chaos around WannaCry/WannaCrypt and why so many businesses have been affected. As I've told others, here's what it boils down to:
- If you keep your PCs and servers up to date on a monthly basis, you're OK.
- If you back up all your data automatically and test the backups from time to time, you'll be OK. It'll still be a pain if you get hit, but at least you won't go out of business.
If own a business and you're not sure about either of these things, then you have reason to panic.