Spam is big business, and economics are in the bad guys' favor. Say a spammer blasts 100 million messages. If just 1% get through, and 1% of those are answered, that amounts to 10,000 responses. No other advertising is as cost-effective, so to win we must turn the economics of spam around.

Problem is, anti-spam systems lose effectiveness as the volume of e-mail increases. Filters may be just as successful as always, says Greg Olsen, director of product management at Sendmail. But the rub is that, with twice the spam this year as last, a filter that lets only 10% through will be allowing twice as much junk. Users--including those who sign the checks for new purchases--will notice the increase, and this is keeping anti-spam vendors we spoke with awake at night.

Make no mistake: It's an arms race. Spammers are constantly developing new techniques, employing professional software developers, and investing in technology to create the sophisticated systems needed to evade controls. In 2007, we saw the damage done by botnets, armies of infected computers that enable spammers to avoid the expense of purchasing Internet connectivity and the hassle of having that connectivity shut off once the ISP realizes what's going on. Another dark benefit of botnets is that spam is sourced from many different nodes, making it much harder to choke the flow. The Storm worm, with morphed versions appearing constantly, reflects a new trend of all-purpose botnets, in which infected computers download their tasks from a central controller.

As for technique, image and attachment spam has largely been replaced by link spam. These messages include some teaser text and a Web URL that delivers a one-two punch in that the Web pages often use browser bugs to infect the recipient's computer, adding it to the botnet. With link spam, the botnet tactic pays off twice for spammers, as they can direct part of their botnets to act as Web servers hosting the pages and malicious code.

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