Boxcar
With all due respect with Mixture et al.
What really matters is what the user PC population of China and other parts of the world do.
The statistics are estimates of course, without the margins for error stated, but something like 29 % of all active Internet connected PC's in use are still using XP. A lot! hopefully using revision SP3, which in many ways was a new operating System.
Fixes will still be applied to XP if you are prepared to pay for them.
Some mitigation may be provided by running as a restricted user when accessing the internet, but unfortunately its the normal background processess that are the real threat.
Mixture, among others, has mentioned the API's ie Application Programming interfaces, where human created program code meets the application services provided by the computer operating system.
These families of "low level" programmer / machine interaction functions are by good reason, shared across various versions of Windows and siliarly within other operating systems. Vunerabilities discovered, (not a trivial task) and fixed in later versions of operating systems, can still be leveraged in un patched older versions still used on the internet, causing trouble in their wake.
A glaring example (a much simpller case) is covered elsewhere on the Forums where a user has had the potential hijacking of an email A/C to send spam. Not the users fault, but it still happens - I have been lucky, but a few years back i had the data on a HD destroyed interactively, Anti virus, Firewall and all on XP SP3. That's an old fashioned attack now but the methodology can be used for much greater harm.
The big problem for Microsoft in particular is the persistance in the tail end of the user base still using XP. 13-14 Years on
"It works OK for me - Why change" is the mantra chanted as a barb, in the tech press, but the reality for many users; is that the Computers used represented a significant cost of purchase and cannot be easily be replaced.
CAT III NDB