Spam Research Database saw around 4 million malware spams in the last seven days, and the malware category as a whole accounted for 18% of total spam arriving at our spam traps. The graph below shows hourly spam traffic for the malware category for the past 30 days - note the relatively low levels of activity to the left, and huge peaks on the right, representing the ransomware downloader campaigns. As you can see the campaigns are not continuous, but concentrated bursts, with peaks of 200K emails hitting servers in a single hour. 

[Via]