The volume of malware-infected spam rose nine times between August and September this year, according to Symantec's "October State of Spam" report.
Released Friday, the monthly spam report also indicated that infected spam spiked to 4.5 percent in September. "While the single digit increase may seem relatively small at first, the consequences of this rise is quite significant when you consider that 86.39 percent of all e-mail messages in September were spam," the security vendor said in the report.
One side effect of attached malware is the increase in the average e-mail message size. The method of attaching malware to spam messages as an attack vector more than doubled between August to September, and this trend was correspondingly reflected in an overall increase in message size last month.
Enterprises received fewer e-mail messages between the sizes of zero and 5 Kb, while the volume of e-mail more than than 5k in size was increased. "Larger messages cause a significant burden on IT resources and can delay the delivery of legitimate messages from reaching their intended users," Symantec pointed out.
Last month, an e-mail malware campaign in the United States targeted customers of payroll processor PayChoice. The messages did not carry attachments but directed users to download an infected plug-in or visit a Web site. Malware in the download and on the site exploited holes in Internet Explorer, Adobe Flash and Adobe Reader, PayChoice said.
The overall spam rate in September, however, was observed to have dropped--a finding similarly reported by MessageLabs earlier this week, which said the overall spam volume decreased by 8 percent over the month before.
Symantec also identified a trend of spam coinciding with festive occasions in emerging markets in Asia, such as India. Beyond the "familiar" Halloween and Christmas-related spam, a campaign in India centered around its Diwali festival, it said. Similarly, the recent Chinese Mid-Autumn Festival led to a number of spam campaigns.
Spam origins, according to Symantec, remained largely unchanged in the last month. The top country of spam origin was the United States at 25 percent, with Brazil next at 12 percent. Asian markets India, South Korea and Vietnam each accounted for 4 percent of global spam, whille 3 percent of unsolicited e-mail were found to originate from China.
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