In eleven new documents published by Wikileaks, there is an explanation of a piece of software known as "Brutal Kangaroo." This software suite is used to target "air-gapped" computers by using internet-connected networks within the same organization.

Quartz explains how it all works:

Brutal Kangaroo works by creating a digital path from an attacker to an air-gapped computer and back. The process begins when a hacker remotely infects an internet-connected computer in the organization or facility being targeted. Once it has infected that first computer, what the documents refer to as the "primary host," Brutal Kangaroo waits. It can't spread to other systems until someone plugs a USB thumb drive into that first one.