The welcome news comes in the wake of reports at the start of the year when some experts asked whether the spammers had taken a holiday over Christmas. That trend, however, continued and in March, Symantec reported that spam levels were continuing to decline.
And now the trend has continued apace, something that the IT security vendor attributes to the downing of the Rustock botnet in March.
According to the latest spam report, Bagle - currently one of the largest botnets - has decreased the amount of spam that it sends from 8.31 billion spam emails per day during March to `just' 1.60 billion spam messages per day in June.
Delving into the report reveals that 76.6% of the spam seen in June was sent by botnets, compared with 83.1% in March. All of this resulted in spam accounting for 72.9% of all email seen in June - a figure significantly down on the 90+% levels reported late last year.
Commenting on the figures, Paul Wood, Symantec's senior intelligence officer, said that, despite the decrease in botnet spam this month, spam is still to be considered a dangerous force on the internet.
"Cybercriminals continue to use botnets to conduct distributed denial of service attacks, carry out fraudulent click-thrus on unsuspecting websites for financial gain, host illegal web site content on infected computers, harvest personal data from infected users and install spyware to track victims' activities online", he said.
Wood went on to say that spam remains a huge problem and levels continue to be unpredictable.
Following the disruption of Rustock in March, approximately 36.9 billion spam emails were in circulation each day during April. This number rose to 41.7 billion in May, before falling back to 39.2 billion in June, he noted.
"During the same period last year, spam accounted for 121.5 billion emails in global circulation each day, equivalent to 89.3% of email traffic in June 2010. Over a twelve month period, a drop of 68.7% in volume resulted in a fall of only 16.4 percentage points in the overall global spam rate", he said.