Programming

Well, in a sense you can. Oversimplified:

Create a network that is physically disconnected from everything. You need a DNS server ( 1.1.1.2 which gives the answers to all inquiries as 1.1.1.0, a box called internet (1.1.1.0), a box called test (1.1.1.3).

These can be virtuals on a single server. But. Treat the whole server as poison so - There cannot be any network connection out of the box. Ever.

The US National labs do this to test potential malware. You run the bad guy on test. You run your program on internet to see what traffic you get aimed for where, for example. You then indepedently check "where" against known lists like Tor access points, bad sites in general. There is a blacklist that is updated daily, I believe.

I've oversimplified this a lot. As an example, you need to be able to munge any actual ip request like 8.8.8.8 -> 1.1.1.0. The labs work with dozens of virtuals simulating various sites out in the wild.

This is also done by companies who specialize in security software. I saw a demo by folks from Sandia Labs and a security vendor a while back. Very interesting. The vendor sells the system. Duh.

Once done testing you wipe everything and restore from tape or whatever. The "whatever" cannot ever be seen by the nasty system except after a complete wipe.
The labs also reflash the bios and do some other cleansing.