When Microsoft made Windows 10 publicly available to all users in 2015, it said about five million people had signed up for Windows Insider program, and were using the OS every day. That number has grown to hit 10 million now, it said this week. From a report: Microsoft launched Windows Insider in October 2014 with its first public Windows 10 Technical Preview, and by that December the program counted 1.5 million members. It was a solid start, but the company now says that in just over two years numbers have grown 566 percent to 10 million fans. "We count over 10 million Windows Insiders today, many of them fans, who test and use the latest build of Windows 10 on a daily basis," wrote Yusuf Mehdi, corporate vice president of Microsoft's Windows and Devices Group. "Their feedback comes fast and furious, they have a relentless bar of what they expect, but it so inspires our team and drives our very focus on a daily basis."