A virtual security appliance is a computer appliance that runs inside virtual environments. It is called an appliance because it is pre-packaged with a hardened operating system and a security application and runs on a virtualized hardware. The hardware is virtualized using hypervisor technology delivered by companies such as VMware, Citrix and Microsoft. The security application may vary depending on the particular network security vendor. Some vendors such as Reflex Systems have chosen to deliver Intrusion Prevention technology as a Virtualized Appliance, or as a multifunctional server vulnerability shield delivered by Blue Lane. The type of security technology is irrelevant when it comes to the definition of a Virtual Security Appliance and is more relevant when it comes to the performance levels achieved when deploying various types of security as a virtual security appliance. Other issues include visibility into the hypervisor and the virtual network that runs inside.
Security appliance history Traditionally, security appliances have been viewed as high performance products that may have had custom ASIC chips in it that allow for higher performance levels due to its dedicated hardware approach. Many vendors have started to call pre-built operating systems with dedicated applications on dedicated server hardware from the likes of IBM, Dell and offshore brands “appliances”. The appliance terminology although heavily used now has strayed from its original roots. An administrator would expect to see any underpinning Linux OS employ a monolithic kernel since the hardware platform is presumably static and vendor-controlled. However, the following examples are configured to use loadable kernel modules, reflecting the dynamic nature of the underlying hardware platforms used by product managers. "Appliances" have varying degrees of administrative openness. Enterasys Dragon version 7 IPS sensors (GE250 and GE500) are lightly hardened version of a Slackware Linux distribution, complete with administrative vulnerabilities, and shipping with anonymous root access the preferred method of administration of the underlying OS. Motorola AirDefense management consoles are shipped as an "appliance" without supported root access. Administrative setup tasks are performed via a textual menus running as an unprivileged user. Websense DSS sensor devices use CentOS 5.2 underneath and also allow root access at setup time. McAfee's older e-Policy Orchestator distributions use a RedHat 7 -based distribution, but modifications to typical OS configuration files are reset on reboot. Most of these devices primary configuration are via web interfaces. The implication that patches are not required for appliances is less accurate than the implication that vendors will be less apt to provide swift modular patches without complete reimaging of the devices. Companies such as NetScreen Technologies and TippingPoint defined security appliances by having dedicated hardware with custom ASIC chips in them to deliver high performing Firewall and Intrusion Prevention technology respectively. These companies defined their specific markets in the early 2000–2004 time frame.
Modern day use of the term Security appliances during that time not only had custom ASIC chips and dedicated hardware but also was delivered on hardened operating systems and had pre-install security applications. This capability delivered performance as well as ease of installation and as a result, software vendors began calling pre-installed security applications on general purpose hardware, “Security Appliances”. This model became so appealing that pure software vendors such as Stonesoft or CheckPoint Software began shipping pre-built operating systems with their security applications after a long history of selling software that had to be installed on existing customer hardware and customer operating systems. With the explosion of virtualization technology that has brought on the ability to virtualize hardware and create multiple software computer instances, it became apparent in 2005 by security vendors that a new method of deploying their security appliances was on the horizon. For the first time in history a vendor could now deliver a hardened operating system with a pre-installed security application that promised ease of deployment without having to couple a dedicated hardware device.
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