Spam levels have dropped massively in recent months, though researchers fear this is simply because botnet operators have switched their attention to more lucrative activities.
Junk mail volumes - which reached 90 per cent last summer - are down to 75 per cent this summer, net security firm Symantec reports.
The 15 percentage points drop in spam has led to a 60 per cent decrease in total email volumes, helping reduce network congestion and server load in the process.
Symantec reports that junk mail volumes that reached a high of 230 billion spam messages per day in July 2010, 90 per cent of all email traffic, are down to 39.2 billion messages per day, 72.9 per cent of all email.
The net security firm credits the dismantling of the infamous Rustock botnet, as well as the closure in September 2010 decision of equally infamous unlicensed pharmacy affiliate operation Spamit, for the overall decline in useless time-wasting messages littering our inboxes.
The operators behind Rustock - blamed for 47.5 per cent of all spam, or around 44.1 billion junk mail messages per day - took a break in December 2010. Junk mail operations resumed at a slightly lower level in January, but these activities were brought to a halt by a successful takedown operation in March 2011.
Security watchers feared at the time that other spam-sending botnets would step in to fill the junk mail void, but this prediction has failed to pan out. For example, the amount of spam sent by one of the remaining spam-sending botnets, Bagle, has actually dropped from 8.31 billion spam messages per day in March 2011 to 1.60 billion per day in June 2011.
The volume of compromised machines that make up botnet networks hasn't decreased anything like as much, if at all. Instead fashions in the digital underground have changed so that these machines are now being abused to run denial of service attacks instead of for junk mail distribution, Symantec reports.
"This decrease in spamming activity may be evidence that increased investigation of the spam underworld has both disrupted the affiliate networks, such as Spamit, that pay for spam campaigns, and led to botnet controllers looking to keep their heads down so as not attract the attention of a legal investigation by sending large volumes of spam," Symantec analyst Martin Lee explains.
"Interestingly, during the same period there has been a reported rise in distributed denial of service attacks, which can also be undertaken by botnets. It may be that the botnet owners are looking to other modes of operation to maintain their revenue, while moving away from the now less profitable and more risky business of spamming."
A blog post by Symantec charting the decline of junk mail volumes can be found here. ®