Malware now infesting my primary computer:

Of course the only way to be totally safe is to never switch on your computer. But a VM is an additional safety barrier because the vast majority of malware is not able to escape a VM (of course it also depends on your setup; if your VM networks with your host OS, then of course the standard network infection paths are open, so any worms might spread to your host this way; also you should be careful with files transferred from the VM to the host). Even better if your host and guest are different operating systems: Then only cross-platform malware can infect the host from the guest.