The article states "Installed on the Windows machine", the Silverback software is actually installed on one single windows machine, which performs all the polling of network, systems and applications on the network that one windows box can see. The polling results are forwarded to a central station over the https vpn established between the one windows station and the central server. The solution is both agentless and free of vpn software configuration. If you can make an outbound https connection, you're in business.