Botnets are networks of computers that have fallen under the control of cybercriminals, capable of accumulating revenues of millions of pounds per year – and it's possible that your PC be 'one of the gang' without your knowledge.

On 11 February 2008 a US teenager (cybername: Sobe) pleaded guilty to surreptitiously installing adware on hundreds of thousands of computers. The machines had been hijacked and enlisted into a network of computers known as a ‘botnet’.

Botnets are networks of computers that have fallen under the control of cybercriminals. Such villains use these networks for malicious purposes, and the owners of the affected PCs remain none the wiser to their system’s underworld antics. According to Symantec, home users account for 95 percent of all botnet PC owners.

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The truth about your PC

Botnets are mostly used to send spam and harvest private data from infected machines, but can also be used to deluge websites with data to knock them offline and to host phishing sites and other illegal content – the possibilities are endless. "[Botnets] make easy money for the controller and are in huge demand," says DC Bob Murls, of the Met’s police computer crime unit.

The ease with which a budding cybercriminal can get hold of necessary technology has led to growing concern among law-enforcement agencies. Bot controllers (or ‘herders’) lease their networks to spammers and criminals for commercial gain, and it’s a lucrative business – those with an interest in accessing thousands of machines will pay highly for the privilege.

US investigators estimate that the revenue from botnets in America runs into hundreds of millions of dollars a year, and the size of the problem is increasing at an alarming rate; the FBI has identified at least one network that consists of more than a million PCs.

It all sounds pretty frightening. Having your machine hijacked for nefarious purposes certainly doesn’t sound like a lot of fun – even less so when you consider the amount of personal data that’s stored on the average home computer.

It’s not a one-sided fight. As the criminal fraternity rushes to embrace the botnet, law-enforcement agencies are hot on their heels. The result is a technological arms race.

Murls, who spends most of his time breaking botnets, describes himself as being on the "bleeding edge" of the battle with hackers, and botnets are a top priority.

"Botnets are an emerging threat," he said. "They’re complex investigations, they’re very time-consuming and they cross international boundaries, but we’re making progress."

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Botnets are networks of computers that have fallen under the control of cybercriminals, capable of accumulating revenues of millions of pounds per year – and it's possible that your PC be 'one of the gang' without your knowledge.

What can be done?

Nobody who uses the internet can afford to ignore the danger. But there are some basic steps you can take to protect yourself.

  • Use antispyware and antivirus programs, and ensure they are updated once a week.
  • Install a firewall and turn it on.
  • Keep your operating system patched with the latest updates and fixes.
  • Take time to educate yourself and your family about the risks – computers used by children are particularly vulnerable.
  • Monitor your PC’s performance; be alert for any sign of a slowdown. There may be no cause for alarm, but it’s wise to find out. Visit our forum and ask for advice in the Helproom if needed.

Botnets are a sinister addition to the range of security threats facing us all as we surf the web; we ignore them at our peril. Our last word goes to John Walker, security expert and visiting professor at Nottingham Trent University: "When you buy a router it should come with a health warning."

Visit Security Advisor for the latest internet threat news, and internet security product reviews