This us why you use cloud backups not simple network shares for backups so there is no easy way to infect and wipe the backup history :)Not so easy when your servers are breached ... [ LINK ]Try not to open dodgy files and have backups.That's the easier way to keep your files safe.
The best kind of backup you could have is compressed incremental virtual machine images as the image is captured outside the virtual environments and cannot be messed with by a virus in the vm. Not only that but vms have a lot of other advantages such as easy migration to other hardware in event of a failure...
A bigger question regarding your link is how on earth the virus was able to encrypt the databases on the server from a workstation? A database like this should be accessible only via a database protocol for example on port 1443 for mssql via a client program, or even better via a Web app on port 443 on an intranet. If the workstations are able to directly access and worse change those files over the network this smells of shoddy access control and the police departments should be frankly ashamed of themselves...
