The volume of spam messages sent to web users around the world fell in the third quarter of the year, but those mailings that did get through presented a bigger danger.
This is the conclusion of a new report by Kaspersky Lab, which shows that spam volumes dropped by 2.8 per cent between July and September 2012 compared to the same period last year.
At the same time the share of malicious mailings rose from three per cent of all spam in the third quarter of 2011 to 3.9 per cent during the corresponding quarter this year.
Kaspersky Lab said that the decline in spam could be down to a seasonal summer slowdown in business. However, changes in the advertising industry could also be playing a part.
Indeed, messages are now shifting from email to other mediums, including banner ads, coupon services and social media advertising.
Darya Gudkova, head of content analysis and research at the security firm, said this migration of advertisers may be due in part to the growing criminalisation of spam.
"Over the past year, Kaspersky Lab experts have observed two trends in parallel: a decrease in the percentage of spam and a slight rise in the percentage of malicious mailings," she remarked.
"More likely than not, both trends will continue, as the percentage of spam is on the decline due to the migration of advertisers of legitimate goods and services to other venues."