The first quarterly report from Message Labs for 2011 sends mixed signals about the state of spam. With the Rustock botnet being killed off in March (followed by the Coreflood botnet this month), spam email distribution is down, but accoridng to Message Labs the amount of data traffic attributed to spam is on the rise.
The reason, it seems, is a spike in the use of ZIP file attachments as a vector for distributing malware in spam email messages. So, even though there are fewer spam email messages overall, more of those messages have ZIP file attachments making them consumer more network bandwidth.
Check out the full Message Labs March 2011 Intelligence Report for more about the rise in ZIP file spam, and to learn more about current trends in spam and malicious email.