One botnet is now sending over 60 billion spam messages every day, according to researchers at Marshal, and it’s one you’ve probably never heard of -- Srizbi.

Srizbi was also ranked as the largest spamming botnet last month by researchers at SecureWorks, but for the most part it has been overshadowed by the better-known Storm and Kraken and/or Bobax botnets. (See SecureWorks Unveils Research on Spamming Botnets and New Massive Botnet Twice the Size of Storm.)

Srizbi now sends more spam than all other botnets combined, according to new research from Marshal’s TRACE team. In comparison, Storm is producing only about 20 percent of all spam, according to the research. SecureWorks last month reported that the world’s biggest spamming botnets together send over 100 billion messages a day.

“Mega-D (a.k.a. Ozdok) was the number one spammer earlier this year, in January, but was replaced by Srizbi since February,” says Glen Myers, sales engineer for Marshal. Srizbi mostly sends spam promoting herbal remedies and male enhancement spam, along with items such as watches and pens, he says.

“Srizbi typically attempts to spread itself through spam campaigns, often using celebrity ‘news’ as lures,” Myers says. Marshal has counted around 300,000 bots in Srizbi; SecureWorks has Srizbi at about 310,000 bots as of last month.

The spamming botnet encrypts its command and control and is infamous for its advertising links to porn-related video files of celebrities, which are really malware that aims to infect PCs and recruit them as bots, according to SecureWorks researchers.

“The challenge now is for the security industry to 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 Bradley Anstis, vice president of products at Marshal.

Marshal says Srizbi’s surge came when Mega-D’s C&C servers went offline for 10 days in February after it had been exposed. “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,” Anstis said.

— Kelly Jackson Higgins, Senior Editor, Dark Reading