If you’re using ad-blocking technology on your smartphone, you’re not alone. Some 2.5 million Americans are employing mobile browsers and other tech on their devices to avoid unwanted ads, but that’s nothing compared to the vast number of consumers blocking ads in China, India, and Indonesia.

This is according to new data from PageFair, which reports that the use of mobile adblocking browsers — which have a default setting of blocking all ads — grew by 90% in 2015 alone, with some 408 million people using them worldwide. That’s around 21% of all smartphone users.

Thing is: Almost all of those users come from the Asia-Pacific region. According to the report, this area only accounts for 55% of all smartphones, but 93% of ad-blocking browsers.

The overwhelming majority of mobile ad-blocking is occurring in just a few countries: China, with 159 million ad-blockers; India (122 million); Indonesia (38 million); and Pakistan (10 million).

Granted, these are all among the world’s largest countries, but other large nations don’t even come close to the same level of adoption. The combined usage in Russia, Saudi Arabia, Brazil, Malaysia, and the U.S. only comes out to about 1/10 that of China, even though these five nations together have a population about half the size of China’s.

It’s not just a population or geographical issue. Asian countries like Japan and South Korea didn’t even make the list of countries with notable levels of ad-block adoption.

So why are users in developing countries clamoring for ad-blockers while others are not? The authors of the report theorize that it has something to do with the relative cost for data. Just like everything else you see on your phone, ads use up data, so if you can block the ads, it should free up more data for the content you actually want.

“Adblocking browsers will continue to grow wherever data costs are high,” reads the report. “Unless the bandwidth cost of current advertising is addressed, the ad-funded digital media industry will never get a chance to flourish in many developing economies.”

Though the U.S. is just testing the waters with regard to mobile ad-blocking the authors do note, that Western countries have a high rate of ad-block tech on their desktop computers, indicating a desire to keep these ads out of their lives, and this “may easily shift to mobile unless advertising practices change.”

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