McColo was shut down by its ISP on November 11 following a journalist's inquiries about illicit spam activities. Subsequently, the volume of spam around the world fell by as much as 70 percent since command and control servers for three major spam botnets were hosted by McColo.
The Mega-D botnet, famous for sending billions of spam emails promoting sexual performance remedies, along with the Srizbi and Rustock botnets was effectively turned off due to the closure of McColo. The botnet's thousands of infected zombie computers could no longer communicate with the Mega-D command and control servers and ceased spamming.
However, Mega-D's creators have worked constantly over the past three weeks to set up new command and control servers and re-establish connections with their network of compromised bots. According to the TRACElabs spam statistics, the spammers have managed to restore those connections and Mega-D is now back spamming again.
Marshal8e6 maintains a Spam Volume Index on its website, tracking the total volume of spam it receives. This index is used to measure fluctuations in global spam volume over time. According to Marshal8e6, the volume of spam has doubled since the low point immediately following the McColo shutdown.
Phil Hay, lead threat analyst for the Marshal8e6 TRACElabs said:
Spam from Mega-D has been ramping up over the last few days and reached up to 48 percent of all the spam we captured in our honey pot spam traps. Many security researchers, including ourselves, predicted that spam volumes were likely to eventually bounce back after McColo's shutdown. Based on what we have seen from Mega-D this week, that seems to be happening now. Spam volumes are still only about 40 percent of where they were in September this year but they have doubled since the last week of November, so the spammers seem to be clawing their way back.