Attachment spam on the rise

Attachment spam is on the increase and is eclipsing image-based spam, according to new research.

Findings from IT security company Marshal point to a 25 per cent increase in the level of spam containing attached PDF, Excel, text and zip files within the space of a week. Previously this new trend in unsolicited junk mail only accounted for two per cent of spam.

Experts at the company said the rise in this type of spam corresponds with a decline in image-based spam.

"The latest statistics would suggest that spammers are increasingly favouring PDF spam over image spam," said Bradley Anstis, product management director of Marshal. "However, spammers are also experimenting with a range of other attachment types in an attempt to identify which is most effective."

"The research indicates that one core group of spammers is responsible for the significant majority of attachment spam. All the signs are that it is the same group of spammers behind the Storm worm," said Anstis.

The company noted within this trend the use of Excel attachments in spam emails. While the Excel files are not malicious, but they potentially could be. A number of high-profile vulnerabilities exist for unpatched versions of Excel, and it would be a relatively simple matter for a spammed Excel file to contain an exploit as well as delivering spam, according to researchers at the company.

According to statistics from managed email security company SoftScan, the amount of spam has crept up again. It found that 91.52 per cent of all email scanned during July was spam. SoftScan said despite the change in tactics by spammer to use attachment spam, the rise was down to less legitimate business email being sent as people go on holiday.

"Around this time of year we always see an increase in spam. However, further investigation of the data shows that it has not increased in real terms, but that legitimate email has decreased," said Diego d'Ambra, chief technical officer of SoftScan.

He said that spammers changing tactics around this time of year is bad news for businesses that don't have adequate protection. "Spam that was once stopped before it reached those users' inbox is now getting through, leaving the holidaymaker returning to not just a full work load, but an inbox full of junk mail too," he said.

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