14 DAY TRIAL // According to a report from email security vendor AppRiver, despite the spam traffic being on a descending trend during the past month, there was a huge spike in the number of infected emails.
"Even though overall spam volumes were down slightly during the month of September, we saw a huge increase in malware distributions beginning mid-month with a peak of nearly 11 million pieces delivered in one day," AppRiver researchers write [pdf].
Some widespread threats like the "Here You Have" mass-mailing worm were amongst the primary factors that contributed to this unusual increase.
That particular attack, which distributed a malicious .scr file and affected mostly corporate systems, accounted for 9% of all spam traffic during its run.
Another widespread campaign, which generated emails with random subjects, carried malicious HTML attachments, that redirected users to rogue websites.
The regular Oficla, Bredolab and ZeuS trojans, which come inside archives attached to socially engineered emails, have also made their presence strongly felt, during the past month.
As far as malicious attachments go, three different variants of the aforementioned HTML redirector-type scripts were the most frequently detected and blocked email-borne threats in September.
A variant of Sasfis (another name for Oficla) was the next most prevalent malware. The fact that a separate verison of this trojan also appears in the stats, suggests the increased aggressiveness of campaigns pushing this malware.
Oficla is a trojan downloader, that is part of pay-per-install scheme and is commonly used as a distribution platform for rogue antivirus software.
Another type of junk of emails that saw a significant rise during the previous month, was the so called image spam. This is a relatively old technique aimed at tricking simple anti-spam filters.
The AppRiver researchers point out that while it's not uncommon to see this method being used, the daily rates of such spam increased by almost 900% after September 10th.
In regards to spam origin, the vendor says that Europe was the most spammy continent, accounting for 35.8% of all unsolicited email traffic. Asia follows closely with 33.4% and North America took the third place with 14.9%