Data from Microsoft's Windows Genuine Advantage Program shows that 22.3 percent of Windows installations aren't genuine:
Since WGA launched in July 2005, over 512 million users have attempted to validate their copy of Windows, Microsoft said. Of those, the non-genuine rate was 22.3 percent. 56,000 reports have been made by customers of counterfeit software, which grants that user a free replacement copy of Windows.
While high, that number is less than the average software piracy rate around the world, according to the Business Software Alliance. The BSA reports that 35 percent of the world's software is pirated (22 percent in North America specifically), and a Yankee Group study noted that 55 percent of organizations report instances of counterfeit or pirated software.