Just six botnets were responsible for 85 percent of all spam in February.
This is ,the first time so few botnets have been responsible for so much spam, according to security provider Marshal's Threat Research and Content Engineering team (TRACE).
One botnet alone, dubbed Srizbi, was responsible for 39 percent of spam. It was followed by the Rustock botnet (20 percent) and the Mega-D botnet (11 percent) which returned with a vengeance after the discovery of its control servers saw its spam levels drop to zero during mid-February.
The 35,000 strong Mega-D was inactive for 10-days in February but still accounted for 11 percent f spam during the month, said Bradley Anstis, vice president of products for Marshal.
"Mega-D at its peak last month, it was responsible for a third of all the spam we caught in our spam traps. While the recent publicity spooked the Mega-D spammers into taking their control servers offline, they have now clearly re-established themselves elsewhere," Anstiss said.
Anstis said the Srizbi botnet is using advanced and extremely stealthy malware, garnering most of its success by using celebrity content to lure victims in.
"By highlighting these spam botnets, we hope the security industry can collectively target these major spamming sources and in doing so significantly reduce spam volumes."
The Storm botnet, which attracted significant levels of publicity in recent months and was touted as the world's largest botnet, accounted for only 2 percent of spam for the month of February.
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