Spam evolution: July-September 2009, the latest report from Kaspersky on spam volumes and techniques, found a direct correlation between economic conditions and the content of spam.

The economic downturn has caused spammers to lose some clients, meaning that they have had to advertise their own services in self-promotional spam mail to garner business. The easing economic conditions have led to a resurgence in spam advertising goods and services offered by the spammers' clients, indicating that the spammers are now getting enough business, and no longer need to advertise their own services to potential clients.

The percentage of spam as a proportion of overall mail traffic fell during the summer months, following a traditional pattern. In September, the spam volume began to spike once more.

"A peak of 91.3% was recorded on September 27, with a low of 76.3% on August 1 - this being the only instance during the quarter when the level of spam dropped below 80%", the report said.

Phishing emails increased by 0.5% to average 1.77% of the total volume of mail traffic, the report said, highlighting a new tendency among phishing scammers to use telephone numbers instead of bogus URLs to collect account information.

Other trends included a return to previous filter-dodging techniques by spammers, including HTML tables, and the embedding of background noise into contact information.

The return to HTML, also partly sparked by a preoccupation with message appearance, led to an 8.2% increase in HTML-based spam mail compared to average figures for the first half of the year. "In addition, HTML format makes it easier for the spammer to conceal the target URL from an inexperienced user", the report added.