Wolfgang Gruener took the trouble to graph data from either Net Analytics or Net Market Share.com
(I'm guessing it's really the latter) to illustrate the popularity of recent Windows versions. The main story seems to have nothing to do with the graphs: 66% Of All Windows Users Still Use Windows XP.
While Windows XP was more secure than the systems it replaced, Vista and Windows 7 are much
more secure than XP. Or, at least, it's easier to lock down a Win 7 desktop than an XP desktop and still have a usable system.
Mobsters on distant continents can break into business desktops and transfer funds to money mules. No doubt some of the victims are running the newest OS software, but I suspect the vast majority involve Windows XP, if not even older systems.
Windows XP was introduced at about the time Bill Gates discovered that security was the long pole in the OS tent. Site and desktop penetrations were becoming serious enough to threaten routine commercial applications. So XP introduced a handful of improvements to make it slightly more secure than Windows 2000.
Windows Vista and Windows 7, however, introduced in-depth changes to how the OS controlled critical assets. While typical XP machines allowed almost anyone to install software, Vista and Win 7 restricts software installation in many ways, reducing the risk of back doors, botnets, and root kits.
I'll bet there are more statistics out there to reflect the prevalence of outdated operating systems in security incidents.
To get back to the statistics, XP use has been in a nose dive for months. Overall Windows
use has been in a nose dive for months, too. Growth is being picked up by "other" operating systems and by the iPhone/iPad IOS, suggesting that palmtop devices are driving OS growth these days.