Open source vendor Untangle has come up with a new version of its gateway that can turn any Windows XP PC into a fully-featured security appliance.

Basically a scaled down version of the company's Linux-based Untangle server, the new 'Re-Router' system puts itself between the network's main router and other PCs, filtering all traffic for a range of security threats.

While all routing functions - including fixed IP addresses and NAT (Network Address Translation) - remain the domain of the main gateway, the Re-Router takes over a range of security functions such as content filtering, anti-virus and anti-spam. If the Re-Router goes down, traffic reverts to running through the original gateway without user intervention until the Untangle box reappears.

The anti-virus uses Kaspersky and the open source ClamAV, with the other security features - intrusion prevention, web filtering, firewalling and VPN - being carried out using open source-based apps tweaked by Untangle. The anti-spam element is a mixture of Bayesian filtering, real-time block lists, and the open-source Razor.

Untangle even claims that the PC used to run all this can continue to be used as normal.

As might be guessed from the concept, the free-to-use software is only suitable for use on small networks, up to around 25 users in size, which would otherwise have to employ several appliances in addition to the main router in order to get the same level of security. The company sees the product as appealing to small companies unable to afford hardware investment and possibly lacking the in-house expertise to configure and manage them.

"For small businesses running Windows, our new Re-Router technology offers a free and totally painless way to leverage all the best networking apps," said Untangle's CTO, Dirk Morris. "There isn't any network reconfiguration or re-cabling, just download the software and you're off and running."

As has become an Untangle speciality, the product is free to use, with the company making money from a professional package of services that covers live support, Active Directory support, more policy management, and configuration backup. It's not clear whether a 25-seat network would need much of this extra handholding at any price, but some networks on the threshold between the Re-Router and the higher-end Untangle Gateway might welcome shopping for upgrades.