Virtual machines are a great tool to run untrusted piece of software and analyzing the network activity. Most of the time, the default networking configuration uses a bridge to allow VMs to communicate. One caveat about this approach is that both the VM and the host will access the same network (like a personal trusted LAN for instance…), something definitely not desirable.
Multiple solutions exist to isolate the untrusted VMs from the host LAN. A few years ago we spoke about JanusVM which is no longer maintained and not so easy to set up.
