Picture this: a sneakier kind of spam

SAN FRANCISCO — A new strain of spam popping up in e-mail boxes is confounding consumers and corporate security officials.

The spam contains images spouting everything from stock scams to Viagra, and its volume has more than doubled since April, according to analysis by anti-spam vendor IronPort Systems.

Image-based spam now accounts for 21 percent of all spam, compared with just 1 percent in late 2005, IronPort says. Marketers are deploying image-based spam because it is harder to detect than text-based spam, and consumers are more likely to read an e-mail with a picture or graphic, says Craig Sprosts of IronPort. The newest spam uses technology that varies the content of individual messages — through colors, backgrounds, picture sizes or font types — so they appear to be distinct to spam filters.

The spam is delivered to consumers and companies through millions of compromised PCs, called “bots.” As a result, the messages are like snowflakes: No two are alike, says Julian Haight, founder of anti-spam organization SpamCop.

The spike in new spam has largely eluded software filters and eaten up space on e-mail systems because each message is more than seven times larger than regular spam, Sprosts says. Most image-based spam comes in the form of stock scams, which contain the same basic language within a shaded box. Much of it comes from spam gangs in the USA and Russia, Sprosts says.

The new spamming tactic is the latest salvo in the long-pitched battle between junk e-mailers and filter developers.

“It is a never-ending cat-and-mouse game,” Alperovitch says. The spammers “just pulled another trick out of the hat.”