A single botnet has grown so dramatically in the last two months that it now accounts for half of all the spam, according to new research from Marshal's TRACE team.
The Srizbi botnet has steadily increased its network since the beginning of 2008 and is now the world's largest spam botnet.
"Srizbi is the single greatest spam threat we have ever seen. At its peak, the highly publicised Storm botnet only accounted for 20% of spam. Srizbi now produces more spam than all the other botnets combined," said Bradley Anstis, Marshal Vice-President of Products.
Srizbi is estimated to comprise at least 300 000 compromised computers and sends more than 60 billion spam messages per day. Recently the botnet has been used to promote a range of products including watches, pens and male enlargement pills. Srizbi also actively distributes copies of its own malware in malicious spam campaigns using social engineering ploys to trick recipients into infecting their computers.
"Microsoft recently announced its success combating the Storm botnet with their Malicious Software Removal Tool (MSRT). The challenge now is for the security industry to collectively turn its sights on Srizbi and the other major botnets. We look forward to seeing Microsoft target Srizbi with MSRT in the near future," said Anstis.
In January, Marshal announced findings that the infamous Storm botnet had lost its place as the number one source of spam to the Mega-D botnet, otherwise know as Ozdok. Marshal's latest data shows that Srizbi's rise to prominence in February coincided with the decline of the Mega-D botnet after its control servers were taken offline for 10 days.
"It is difficult to say for certain why Mega-D went offline after we announced our findings. It is probable the spammers got spooked and decided to lay low for a while. Security researchers were close to discovering their control servers when the plug was pulled. Typically the spammers like the 'low and slow' approach; building their botnet up over time and trying to stay under the radar to avoid detection. It is an intriguing chain of events that, as Mega-D went offline, Srizbi stepped in to fill the gap and hasn't looked back since," said Anstis.
Mega-D quickly bounced back and regularly jostles with the Rustock botnet for second place in Marshal's spam statistics. Marshal's TRACE researchers have observed individual computers infected with the Rustock malware sending as many as 25 000 spam messages an hour.
"While other botnets such as Rustock might be smaller in terms of the number of compromised computers under their control, they can be very efficient at sending spam," added Anstis.
Marshal's charts and statistics depicting botnet activity over time can be found on the TRACE Centre: http://www.marshal.com/trace/spam_statistics.asp.
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