The amount of spam carrying embedded images designed to
evade filters has doubled over the past three months, security
experts have warned.
Messaging security firm CipherTrust warned that at peak times,
the devious image-based spam accounted for more than 30% of all
spam messages.
The increase has come as spammers have developed new tools that
can generate completely randomised images and deploy them in spam
at speeds of up to one million an hour.
Overall, malicious message volumes have been rising sharply,
with a 20% spike in global mail volumes last month, CipherTrust
said.
The security firm also warned that the number of “zombies” –
compromised PCs used to pump out spam, viruses and phishing frauds
– was continuing to increase, with the number of newly created
zombies shooting up by 20% in May alone, the last major spike in
numbers.
CipherTrust chief technology officer Paul Judge said: "Over the
last four years, the people responsible for spam have continued to
use aggressive, and frankly ingenious, techniques to make their
messages blend with legitimate e-mail.
“It is a high-stakes, high-profit business, and they continue to
invest heavily in attempts to get messages delivered to users in
the face of increasingly effective anti-spam systems. The growing
use of zombies and image-based spammers are examples of these
initiatives.”
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