Much of that flood is made up of a nettlesome new breed of junk e-mail called image spam, in which the words of the advertisement are part of a picture, often fooling traditional spam detectors that look for telltale phrases. Image spam increased fourfold from last year and now represents 25 to 45 percent of all junk e-mail, depending on the day, Ironport says.

The antispam industry is struggling to keep up with the surge. It is adding computer power and developing new techniques in an effort to avoid losing the battle with the most sophisticated spammers.

It wasn’t supposed to turn out this way. Three years ago, Bill Gates, Microsoft’s chairman, made an audacious prediction: the problem of junk e-mail, he said, “will be solved by 2006.” And for a time, there were signs that he was going to be proved right.

Get the full story at The New York Times