Android (operating system) store, and by September 2013, one billion Android devices have been activated. , the Google Play store has over 2.7 million Android applications published, and , apps have been downloaded more than 65 billion times. The operating system's success has made it a target for patent litigation as part of the so-called "smartphone wars" between technology companies. Android devices account for more than half of smartphone sales in most markets, including the US, while "only in Japan was Apple on top" (September–November 2013 numbers). At the end of 2013, over 1.5 billion Android smartphones have been sold in the four
Usage share of operating systems and use both. Conversely, sales underestimate usage by not counting unauthorized copies. For example, in 2009, approximately 80% of software sold in China were due to copyright infringement. In 2007, the statistics from an automated update of IE7 for registered Windows computers differed with the observed web browser share, leading one writer to estimate that 25–35% of all Windows XP installations were illegal. The usage share of Microsoft's latest client operating system Windows 10 has been slowly increasing since July/August 2016 (while Windows 7 has had a slight decrease at the same time), reaching around 27.15% in December 2016. Windows