You install the software on a single Windows machine, which then scans the network to discover all devices (servers, workstations, laptops, mobile devices, virtual machines, routers, switches, and printers) and interrogate them regarding security issues. Once discovered, the devices can be managed with or without an agent; using an agent will give IT administrators deeper results. While no security tool is a silver bullet, GFI LanGuard is attractive because it's notably more mature than many security tools popping on the market and so has a feature depth you won't find in many other platforms.
In addition, it enables complete Patch Management of security and non-security patches to Microsoft operating systems, MAC OS X, major Linux distributions and third party applications. It can also automate patching for all major web browsers.