Who are the biggest ad blockers? by Philip Elmer-DeWitt @FortuneMagazine September 21, 2015, 3:03 PM EDT E-mail Tweet Facebook Linkedin Share icons Despite the apocalyptic rhetoric that accompanied the release of iOS 9, it’s still early days in the ad block wars. According the best available data—a PageFair/Adobe report issued last month—only 6% of Internet users around the world are actively blocking ads. But the phenomenon is growing quickly. Adblock use last quarter grew 41% worldwide year over year and 48% in the U.S. As of Q2, 45 million Americans were using ad blockers. Who are these people? They are mostly men. In a 2014 survey, men were 48% more likely than women to use adblock plug-ins when browsing. They are largely millennials. Peak usage is with 18-29 year olds, 41% of whom claim to use adblock software. They tend to live in the Northeast and Pacific coasts. Oregon has the highest ad blocking rate at 16.4%. Washington DC, at 8.2%, has the lowest. They’re not on mobile devices. Smartphones and tables represented 2% of adblock use in Q2 2015, desktops and laptops represented 98%. . Ironically, given that online advertising accounts for 90% of Google’s revenue, it’s Google Chrome, not Apple’s Safari, that’s been driving most of the adblock growth. Ad block use on Google’s browser increased 51% from Q2 2014 to Q2 2015, reaching 126 million average monthly active users. According to PageFair and Adobe, the economic cost of ad blocking—in terms of lost ad revenue—will top $21 billion in 2015 and nearly double again next year. “This has the potential,” the report concludes, “to challenge the viability of the web as a platform for the distribution of free ad-supported content.” Follow Philip Elmer-DeWitt on Twitter at @philiped. Read his Apple AAPL coverage at fortune.com/ped or subscribe via his RSS feed.