Botnets continue to dominate the spread of spam and malware, and spam levels as a proportion of all traffic are up over last year, the latest MessageLabs report reveals.
Botnets were responsible for 87.9% of all spam in the third quarter, up 2.9 percentage points over Q2, the report said.
MessageLabs found that while the ratio of spam in email traffic had fallen slightly in August, the average for Q3 was 88.1%, up from 81.0% a year ago.
It said Rustock, one of the oldest and largest botnets, has doubled in size since June, with 1.3 to 1.9 million bots. A newer botnet, Maazben, has grown quickly since first discovered in late May. Sending out casino-related spam, it has accelerated during the past month from 0.5% to 1.4% of all spam.
However, the gangs behind botnets have largely negated the tactic adopted successfully last year of closing down ISPs that host them, MessageLabs said.
Paul Wood, a senior analyst, said because of the advance in technology since late 2008, the most recent ISP closures had taken botnets off-air for only “a few hours rather than weeks or months as before.”
“Over the past year, we have seen a number of ISP’s taken offline for hosting botnet activity resulting in a case of sink or swim and an ensuing shift in botnet power,” he said. “This has undermined the power of the more dominant botnets like Cutwail and cleared the way for new botnets like Maazben to emerge.”