Phatbot arrest throws open trade in zombie PCs

10 cents a PC for access

The arrest of the suspected author of the Phatbot Trojan could lead to valuable clues about the illicit trade in zombie PCs. The arrest of the alleged Phatbot perp was overshadowed by the unmasking of the admitted Sasser author, Sven Jaschan. But the Phatbot case may shed the mostlight into the dark recesses of the computer underground.

Phatbot is much less common than NetSky but is linked much more closely with the trade in compromised PCs to send spam or for other nefarious purposes. Viruses such as My-Doom and Bagle (and Trojans such as Phatbot) surrender the control of infected PCs to hackers. This expanding network of infected, zombie PCs can be used either for spam distribution or as platforms for DDoS attacks, such as those that many online bookies have suffered in recent months. By using compromised machines - instead of open mail relays or unscrupulous hosts - spammers can bypass IP address blacklists.

Phatbot was been used to spam, steal information or perform DDoS attacks, according to Mikko Hyppönen, director of anti-virus research at F-Secure. "You could do anything you wanted with it," he said. Phatbot is a variant of Agobot, a big family of IRC bots. Hyppönen said people were selling tailor-made versions of the bot for various illegal purposes.

NetSky also contains a backdoor component but this was designed only to upgrade malicious code: it is not a conscious attempt by its designer to turn compromised PC into spam zombies, Hyppönen says. Alex Shipp of MessageLabs said hackers ware still able to seize machines compromised by NetSky but he agreed with Hyppönen that worms such as Bagle and MyDoom, and Trojans like Phatbot, are far more commonly used in zombie spam networks.

As reported last month, networks of compromised hosts (BotNets) are commonly traded between virus writers, spammers and middlemen over IRC networks.

The price of these BotNets (DoSNets) was roughly $500 for 10,000 hosts last Summer when the MyDoom and Blaster (the RPC exploit worm) first appeared on the scene. "I have no doubt it's doubled since then as hosts are cleaned and secured," Andrew Kirch, a security admin at the Abusive Hosts Blocking List told El Reg. By his reckoning, non-exclusive access to compromised PCs sells for about 10 cent a throw.

An unnamed 21 year-old man from the southern German state of Baden-Wuerttemberg was arrested last Friday on suspicion of creating the Agobot and Phatbot Trojans. He is yet to be formally charged. ®

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