Next was Facebook with 78 million, followed by Yahoo! (66 million) Amazon (44 million) and Wikimedia, which includes the Wikipedia site (39 million). But it also found that 80 percent of time spent was represented by "app" usage compared to 20 percent via browser.
Twitter saw an even higher percentage of time spent with apps at 96.5 percent of all minutes. The most popular app was Apple iTunes with 32 million users, followed by Google Maps with 29 million and Facebook with 26 million.
Social networking was a particularly popular activity on smartphones, and Facebook led the pack, with the average Facebook mobile user spending more than seven hours via browser or app in March.
Pinterest, which has seen its adoption explode in recent months, reached 7.5 million smartphone visitors who used the brand for nearly an hour.
Location-based social network Foursquare attracted 5.5 million mobile visitors at an average of nearly 2.5 hours, while Tumblr reached an audience of nearly 4.5 million who engaged for 68 minutes during the month.
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