The strange death of the mass mailing virus

We are all zombies now

Mass mailing viruses will go the way of macro viruses and become much rarer next year. Viruses such as Sober and MyDoom are simply not as effective as they used to be, Kevin Hogan, a Symantec Europe manager, notes. "People know it’s risky to double click on viruses. For virus writers there's no technical kudos. Also mass mailing viruses are noisy, bringing attention to themselves, and that goes against the trend of developing malware that hides its presence on infected systems," he said.

Last year Hogan predicted browser vulnerabilities would become less important in 2004: "I've had to eat my words on that. IE vulnerabilities are often used to surreptitiously load malware onto people's PCs. Client side flaws will continue to be important next year."

Once upon a time, Virus writers were motivated by notoriety, but now the profit motive is more important. The use of keylogging Trojans in phishing scams is one way they can make money. Selling access to botnets - networks of compromised machines - is another potential money-spinner, as is adware.

According to Hogan, adware purveyors are becoming more aggressive about getting their code onto PCs. Adware that uses software vulnerabilities to spread, hide itself and that is difficult to uninstall is becoming more common, he says.

Rise of the machines

The first half of 2004 saw a huge increase in zombie PCs. Also called bots, their average numbers rose between January and June from under 2,000 to more than 30,000 per day - peaking at 75,000 on one day, Symantec reports.

Botnets are computers infected by worms or Trojans and taken over surreptitiously by hackers and brought into networks to send spam, more viruses, or launch denial of service attacks. Increased collaboration, at least in development, between malware authors means this problem is likely to get worse in 2005.

Mass mailing viruses such as SoBig and Trojans such as Gaobot (AKA Phatbot or Agobot), Randex and Spybot are used to create botnets. The source code for Gaobot is in the public domain and has been modified and reposted by "thousands worldwide". "Gaobot has a plug-in architecture. If you want to add exploit code there are people to help you modify it," Hogan says.

How to hijack a botnet

The easy availability of "common or shared source malware" makes it easier to develop customised attacks. This pooling of knowledge creates a means for crackers to steal access to compromised machines. "You don't have to go to the trouble of setting up a botnet, you can steal it," Hogan explains. "If you know the IRC channel compromised machines join and the Gaobot command set you can hijack access. You can get compromised machines to run a customised version of Gaobot that logs them onto a new channel."

Symantec reckons virus writers and those who run botnets are two distinct groups.

"It takes a lot of effort to maintain a botnet, keeping a record of which machines are alive and which are dead. Maintaining a botnet detracts from time spent writing new worms and the skills are different," Nolan says. ®

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