The new botnet on the block Srizbi now accounts for half of all spam, according to research from Marshal.
Srizbi has been steadily increasing since the beginning of the year and is now claimed to be the world's largest spam botnet.
It is estimated to have compromised at least 300,000 computers and generated more than 60 billion spam messages per day.
Marshal said that the botnet has been used to promote a range of products including watches, pens and male enlargement pills. It has also been used in social engineering attacks with malicious spam tricking users into infecting their computers.
In February IT PRO reported about how Srizbi had overtaken the Mega-D botnet in distributing the majority of spam, with Marshal commenting on its advanced and stealthy nature.
"Srizbi is the single greatest spam threat we have ever seen," said Bradley Anstis, vice-president of products at Marshal.
"At is peak, the highly publicised Storm botnet only accounted for 20 per cent of spam. Srizbi now produces more spam than all the other botnets combined."
IT PRO also reported a week ago about how the Storm botnet's threat had decreased dramatically, being at five per cent of its original size. Microsoft's Malicious Software Removal Tool (MSRT) was said to be the reason.
However, the same report also said that Srizbi had the potential to follow Storm as the web's most notorious botnet.
Anstis said: "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 near future."
