E-mail security firmSonicWallsaysPDF-, Excel- and Zip-based spam
ison the increase.
During the second quarter of 2007,
PDF spam emerged as a persistent threat, said the supplier.
These types of e-mail attacks typically contain little or no text
in the body, but an attached PDF file containing malicious
code.
SonicWall says the widespread adoption of PDF spam illustrates
the adaptability of spammers in finding new techniques to
counteract
image-spam prevention techniques.
"PDF spam demonstrates the continued innovation in spam
techniques that attempt to bypass anti-spam detection and trick
employees into opening e-mails that give the appearance of
legitimate business letters," said Andrew Klein, senior product
manager for SonicWall's e-mail security division.
"PDF spam is effective because files in PDF format have long
been considered an acceptable way for businesses to transfer
information. Much like
phishing e-mails, spammers have manipulated the trust factor to
get past both technical and psychological defences," he said.
More recently, SonicWall has detected an increasing amount of
Excel and ZIP file spam.
Klein said, "Think about how many times you have fired off a PDF
or ZIP file to someone with no message or a simple note along the
lines of 'here it is'. Spammers are mimicking this behaviour."
As a result, he said, it is difficult to educate email users as
to which emails to open and which to ignore.
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