Robert McMillan, IDG News Service
Spam is again on the rise, led by a flood of junk images that spammers
have crafted over the past few months to trick e-mail filters,
according to security vendors.
Called "image-based" spam, these junk images typically do not contain
any text, making it harder for filters that look for known URLs or
suspicious words to block them.
Instead of a typed message, users will see only an embedded.gif
or .jpeg image file urging them to buy pharmaceuticals or invest in
penny stocks, or buy penis enlargements or whatever.
Antispam vendor Cloudmark says that half of incoming spam on the
"honeypot" systems it puts out on the Internet to lure spammers is now
image-based. "About a year-and-a-half ago we started seeing a little
bit of it, but it wasn't until the past six months that it became a
serious issue for many antispam companies," said Adam O'Donnell, a
senior research scientist with the company.
Image-based spam has jumped from about 1 percent of all spam messages
in June 2005 to around 12 percent today, according to Craig Sprosts,
senior product manager with IronPort Systems.
Its growth is helping to fuel a global resurgence in spamming, Sprosts
said, and helping to avoid 'nuisance filters' which many netters use
to ostensibly to avoid spam.
The total number of spam messages sent daily is up 40 percent since
April, Sprosts said. Much of this new spam is coming from a
"relatively small group of spammers with control over very large
zombie networks," of hijacked computers, he said.
Spammers now generate an estimated 55 billion messages per day,
according to IronPort. A year ago that number was 30 billion e-mail
messages per day.
The combination of greater volume and better techniques has meant more
complaints for network administrators.
"I've had users complaining in the last few weeks about the overall
increase in spam and I've personally noticed an increased rate of spam
and an increase in the percentage of it that's image-based," said
Jonathan Forster, computing manager with the University of Arizona's
Administrators at Avnet have started stripping certain embedded image
files out of all messages, after seeing an uptick in image-based spam
two months ago, said Rob Kudray, manager of messaging services with
the computer distributor.
One other tactic that is helping keep in-boxes full is the spammers'
practice of constantly registering new domains. Of the 35 million
domains registered in April, 32 million were never paid for and
expired after five days, Sprosts said. He believes that many of those
domains were used by spammers to send out their unsolicited e-mail
during that five-day grace period.
This technique makes it very difficult to blacklist e-mail based on
the URLs it contains. "Traditional blacklists and whitelist approaches
just can't keep up with how fast they're registering new domains and
changing the URLs in the e-mail," Sprosts said.
Copyright 2006 PC World Communications, Inc.
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