Overall, the Russian-headquartered IT security vendor notes, spam levels fell by just 2% as a result, but then bounced back soon afterwards.
According to Darya Gudkova, the firm's head of content analysis and research, this could be down to the closure of SpamIt - a large pharmaceutical partner program - and the fact that Rustock, which specialised in pharmaceutical spam, may well have ceased sending out mass mailings at the end of last year.
"It is also possible that the cybercriminals preferred to lie low for a while given the interest in botnets shown by law enforcement agencies towards the end of 2010", she said.
As a result, Gudkova added, the amount of spam detected in mail traffic in the first quarter of 2011 was just under 80%. This was, she noted, a slight increase compared with the previous quarter, but was considerably less than the corresponding figure for last year.
During the quarter, Kaspersky's report says that spammer made use of some tried and tested techniques to avoid detection. Sending out spam emails containing a link to a video clip advertising anti-spammer services was one of them.
Another trick, says the vendor, saw emails that read `Stop sending me spam' allegedly written by an angry recipient. The email was in fact a spammed message with a link leading to a malicious site.
Delving into the 2011 Q1 report shows how the volume of phishing emails was very small and accounted for only 0.03% of all mail traffic, with PayPal and eBay remaining in the unenviable position of being the organisations most frequently targeted by phishers.