Every day, approximately 89.5 billion unsolicited messages (i.e. spam) are sent by computers that have been compromised and are part of a botnet.

Botnets – apart from inundating out inboxes with spam – can also be used for ulterior purposes such as executing DDoS attacks or hosting websites, so understanding the “modus operandi” and size behind the well-known names is a good idea.

Message Labs’ list of top 10 botnets in 2009 reads like this:

Rustock
Rustock frequently sends spam at full capacity for short periods, and then ceases its activity often for days at a time. Between August and September 2009, it controlled between 1.3 million to 2 million bots.

Rustock had accounted for approximately 10-20% of all spam for much of the year, but by the end of 2009 it had increased its dominance and stabilized its output to approximately 18% of all spam. By the end of 2009, Rustock was mostly sending pharmaceutical and medical spam.

Cutwail
Cutwail consisted of 1 million to 1.5 million bots throughout the year, and was responsible for 17% of all spam.

It was responsible for the surge in Bredolab malware, spoofed greetings card emails containing malicious hyperlinks, phishing activities, pharmaceutical spam and spam peddling counterfeit watches.

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