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There is a botnet out there that uses the Tor online anonymity network to hide its command nodes.

Owners of the compromised network of Windows PCs placed their command-and-control server, which uses the common IRC protocol, as a hidden service inside of the Tor (The Onion Router) network. Aside from the use of Tor for extra anonymity and stealth, the zombie network is pretty typical, according to security researchers at German security firm G Data.

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The botnet is capable of lending itself toward either running DDoS attacks, adware or secondary malware distribution, among other scams.

Botnet owners have moved from running a central C&C server (subject to takedown) to using a peer-to-peer architecture over recent years. P2P systems give every zombie in a botnet the ability to issue commands to other drones. However, this introduces other problems for attackers because it creates a means for either rival scammers or the authorities to take over their botnet, unless they build in a strong and difficult-to-apply authentication mechanism into the systems to thwart potential hijacks.

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Tor is an online anonymity service but the technology also creates a handy means to build an IRC server as hidden service, which attackers could potentially exploit.

This novel approach brings all sorts of advantages for zombie PC herders, as G-Data said.

Since the server is anonymous, it cannot point toward the botnet owners’ identity. Botnet control traffic ends up encrypted by Tor, so Intrusion Detection Systems can’t block it. Blocking Tor traffic in general is problematic because there are legitimate uses for the technology, researchers said.

In addition, it is not easy to take down Tor servers, the G-Data researchers said. Although Tor tends to be slow and unreliable, due to built in latency, this minor disadvantage is more than offset by the many advantages Tor offers as a venue for a botnet command server.

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