The number of consumers using ad blocking software worldwide has increased 41% year-on-year to 198 million monthly active users, according to a report published Monday by PageFair and Adobe. While that figure may only represent 6% of the global web population, ad blocking is expected to cost publishers more than $21.8 billion in 2015 in lost revenue. That represents 14% of global ad spend. By 2016, PageFair and Adobe predict the global cost of ad blocking to rise to $41.4 billion. This chart, which chronicles ad blocking growth from 2009 shows how ad blocker use really started to accelerate from 2013. And while the 41% increase this year was down on the near 70% growth PageFair and Adobe reported between 2013 and 2014, it's nevertheless a worrying trend for publishers. Dr Johnny Ryan, PageFair's head of ecosystem, told Business Insider: 'Ad blocking has grown virally along a classic s-curve to 50+ million ad blocking users at the end of 2012, and onward to 198 million at the end of Q2 2015. This viral growth, and the climb up the curve you describe, is explained by our findings in last year's 2014 report (page nine) that the majority of ad block users find out about ad blocking by word of mouth and through their own online research. Ad blocking is a viral phenomenon that will continue.' The rate of ad blocking varies country by country. The US has an estimated 45 million monthly active ad block users, up 48% year-on-year. Across Europe, 35% of the internet population (77 million users) used an ad blocker at least once a month. Greece has the highest rate of ad block usage in Europe, with 36.7% of internet users in the country using ad block software. As per previous research in this area, PageFair and Adobe found that ad block users are typically, young, technically savvy, and more likely to be male. Right now, ad blocking almost always happens via desktop computers, even though 38% of web browsing happens on mobile. Just 1.6% of ad block traffic on the PageFair network was from mobile devices. But ad blocking on mobile could soon become a mainstream phenomenon. Apple's developer documents for its new mobile operating system iOS9, revealed it will for the first time allow app makers to develop ad blocking software for iPhones and iPads. PageFair and Adobe say this could be a 'game changer.' Apple's Safari mobile browser represents 52% of mobile browsing and 14% of total web browsing. By making it easier to download ad blocking software, ad block usage could soar when iOS9 becomes available in the fall. However, as ad tech company Criteo's president and COO Eric Eichmann pointed out last week, users will still need to manually download the 'obscure' software themselves, meaning the iOS9 update might not be as big and immediate a catalyst as feared. As part of their report, PageFair and Adobe surveyed 400 people in the US about the reasons they might start or have started using ad blockers. Of those who are currently not using ad blocking extensions, the misuse of personal information by advertisers and publishers was the primary reason that would convince them to change their mind. Surprisingly, using an ad blocker to improve the speed and performance of web pages was not listed as one of the responses in the report. In a survey of British internet users conducted by the Internet Advertising Bureau UK earlier this year, 54% of respondents said they block ads because they slow down web browsing. But PageFair's Ryan said performance is not as much of a key motivator as some people might think. Just 8% of respondents in PageFair and Adobe's report last year cited performance as their main reason for installing an ad blocker. PageFair has been tracking the growth of ad blocking for three years, and measures more than a billion ad blocking hits each month across its 3,000+ clients' websites. The company provides publishers with analytics to measure how many of their visitors are blocking ads and a system that displays 'adblock-friendly' ads to ad block users.ad Source.