In the two weeks after December 25, spam volumes declined 58% from 80.2 billion spam emails a day to 33.5 billion, reminiscent of declines experienced when California-based ISP McColo was taken offline in late 2008.
The report noted a decline in the Rustock, Lethic and Xarvester botnets, although in the two weeks that Rustock was dormant, it was being used for click-fraud to generate fake referrals for click-through expenses.
"The closure of spam affiliate Spamit was partially responsible for the disruption to spam output," said MessageLabs Intelligence senior analyst, Paul Wood.
"However, there are likely other factors at work, such as consolidation and restructuring of pharmaceutical spam operations, which has led to instability in the market likely to be exploited as a business opportunity by other spam gangs. We expect to see more pharmaceutical spam in 2011 as new pharmaceutical spam brands emerge and botnets compete for their business," he said.
Since the end of 2010, MessageLabs Intelligence has seen shifting patterns related to pharmaceutical spam-sending, the report said.
Previously, the Canadian Pharmacy brand was the most prolific of the pharmaceutical spam brands. However, when Spamit shut down in October 2010, the brand disappeared as affiliates switched to sending spam for other brands.
This story was first published by Computer Weekly