Online advertising is already hurting.
Web ads is about to go mainstream.
But until recently, the sales manager from suburban Boston didn't realize how well it worked. But consumers are annoyed by the new formats, not least because they tend to slow download speeds. That's where ad-blocking software comes in. Marketed under such brand names as AdKiller, AdSubtract and Junkbuster Proxy, the software has been quietly spreading among Web users for the past three years. More than 4 million people have downloaded WebWasher, a Siemens spinoff, and InterMute's AdSubtract expects to have 2 million users by the end of the year.