They recommended not using Windows because it's the least secure operating system and the biggest target of malware and other attacks. The FH exploit targeted Windows. By simply switching to another operating system, you decrease your attack attack surface by an order of magnitude. If you need to use Windows and can't install another operating system like Linux, even in a separate partition for dual-booting, you should run Linux in a virtual machine and conduct your sensitive activities entirely in that virtual machine. You can even get full disk encryption by encrypting the virtual hard disk, which is usually a ~10 GB file on your hard drive. An even safer set up is to use 2 virtual machines and run Tor in one while conducting your sensitive activities, like web browsing over Tor, in the other VM. Basically, all network connections from one VM are run through the other which has Tor. That would make it incredibly difficult to run an exploit against you to obtain your real IP address.