The illicit trade in compromised PCs

Information Security 2004 Investigators are piecing together the complex relationships between the virus writers, middlemen and criminal gangs held largely responsible for the growth of spam in recent months.

Viruses such as My-Doom and Bagle surrender the control of infected machines to hackers. This expanding network of infected, zombie machines 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.

The IP addresses of compromised machines are traded over IRC networks by either the virus authors themselves or middlemen with payments directed towards anonymous online accounts or (less frequently) via Western Union money transfers. In February German magazine c't reported how it was able to buy access to infected machines - commonly described in the parlance of spammers as "BotNets" - from virus writers. The value of the BotNet market remains unclear but the problem is growing and police investigations, assisted by anti-spam activists, into the illegal trade are taking place on both sides of the Atlantic.

Detective Chief Superintendent Les Hynds, head of the UK's National Hi-Tech Crime Unit, told El Reg: "The trade of BotNets on compromised machines is becoming an industry in itself. Organised crime is making use of this industry."

In a conference call that accompanied the announcement of a legal crusade by the US's biggest ISPs against large scale spammers last month, legal officers described a network of middlemen, hackers, 'cut out' companies and criminals (often based in Eastern Europe) that made anti-spam investigations more difficult. The resale of compromised machines is growing more sophisticated with dealers culling lists to offer access to high-bandwidth machines at a premium or even offering trial purchases as sales promotions. Anti-spam organisations are indirectly noticing the effects of this change in sales tactics.

Mark Sunner, chief technology officer at email security firm MessageLabs, said much of the spam it blocks comes from IP ranges allocated to high-speed cable modem or ADSL accounts, such as roadrunner and MSN in the US. MessageLabs reckons two thirds of the spam it blocks originates from computers infected by viruses such as Sobig-F or Bagle. Spam volumes are growing. More than two thirds of the email passing through MessageLabs systems so far this month was spam compared to 53 per cent for March as a whole. ®

Related stories

Trojans as spam robots: the evidence
Sobig-F blamed for massive increase in spam
Big US ISPs set legal attack dogs on big, bad spammers
Mafia recruiting spammers, crackers, AV chief warns
Online extortionists target Cheltenham