You should use a disposable VM to view untrusted files. Simply disconnecting your computer from the internet prevents a malicious file from phoning home and revealing your IP address to an adversary, but that file could be malware that infects your computer and phones home later. It could also get your MAC address (like the FH exploit did) or hardware serial numbers. A disposable VM with no networking protects against all these things, because it uses virtual hardware with fake MAC addresses and serial numbers. Install a Linux distro, which on its own will protect against 99% of malware, and if you think the file is malicious or has infected the guest OS, destroy the VM and the malware is gone. There is still a threat from malware that can break out of VMs, but you're increasing the difficulty a lot compared to the common malware that we see. A Linux VM running over Tor would have provided multiple layers of protection against the FH exploit, for example.