The report claims that Rustock continued to be the leading spam-sending botnet, 41% in August 2010 from 32% in April 2010, but reducing in the number of botnets under its control to 1.3 Million in August 2010 from 2.5 Million in April (2010).

Paul Wood, MessageLabs Intelligence Senior Analyst, stated that the overall volume of spam in circulation fell a little against the previous quarters as most botnets witnessed downfall in the number of bots, as per the news by messagelab on August 24, 2010.

Wood added that one exception was Rustock that reduced its number of botnets, but raised its volume - almost doubling the volume of spam sent from each bot every minute leading to a rise of 6% in spam mails every day.

Moreover, the botnet has stopped using TLS encryption to send spam, which speed up the connections. By switching off the TLS encryption, the botnet can send high volumes of spam in this case, to the tune of 192 spam mails per minute in place of 96.

Besides Rustock, the Cutwail and Grum botnets were responsible for 6.99% and 16.36% of the total spam respectively. The report claims that first detected in 2007, Cutwail sends the maximum number of malware than any other botnet, generally in the form of a zip file attachment.

The researchers said that the worldwide ratio of spam in mail traffic was 92.2% (1 in 1.08 mails). Around 18% of spam came from yet-to-be-classified botnets. Phishing activity increased from 0.1% to 1 in 363.1 e-mails.

Wood claimed that they had witnessed a striking improvement in the activity of usual botnet suspects. In several cases, there could be newer incarnations of existing botnets updated and there were also some brand new botnets starting to come up, as per the reports by messagelab on August 24, 2010.