Botnets are big, bad, and widespread - but if your system is infected, you can take several simple steps to clean it and stay safe. Here's how.

Botnets, or networks of compromised computers, are a growing security menace. Your PC can be recruited into a botnet if you accidentially visit a malicious site and download tainted code disguised as a video. Alternatively, visiting a legitimate site that has been compromised could also result in your machine being attacked.

Once a bot infects your PC, it calls out to its command-and-control (CnC) server for instructions. A bot is similar to a traditional Trojan horse; but rather than merely installing a keylogger or a password stealer (which it might still do anyway), a bot works with other infected PCs, compelling them all to act together, in some ways like a very large computer.

Spammers pay big money to have a bot blast their message to thousands of machines; in particular, Canadian pharmaceutical spam is big at the moment. Other uses for bots include attacks that shut down commercial websites, often paired with a ransom demand.

Brisk business also exists in what's called fast flux. To keep phishing websites active, operators change domains frequently. Botnets provide a quick and easy means to do so, and, according to security firm Kaspersky, botnet owners charge big money for that service.

In July, the ShadowServer Foundation, a group specialising in sharing information about botnets, reported that the number of identified botnets grew from 1500 to 3500 in the last two years. Each of those 3500 networks could contain several thousands of compromised PCs - and any given PC could be infected by multiple bots.

In raw numbers, the United States and China are the homes of most of the bot-infected machines, says Jose Nazario, manager of security research at Arbor Networks.

"I think it's very safe for most PC users to assume they are part of a botnet," he says. "It's a very dangerous internet for most folks."

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NEXT PAGE: What to do if you find a botnet


  1. The rise of botnets
  2. How to find and destroy a botnet infection