On more than one occasion, I have pointed out the error of judging operating system market share and installed base from the monthly Net Applications metrics. It's not that Net Applications is inaccurate, it's just not a measure of the actual installed base.

Net Applications has millions of sensors on websites around the world that take a tally of the operating system being used by each visitor. Therefore, it's not a measure of operating systems installed or sold, but of the ones in use for the period in question, which makes it something of a trailing indicator. Windows XP still shows up despite Microsoft discontinuing sales of the OS years ago.

And once again, a few news outlets got tripped up on this when looking at the December figures. According to Net Applications, Windows 8 usage dropped from 18.7% in November to 13.5% in December.

Meanwhile, XP jumped from 13.6% in November to 18.3% in December, which would qualify XP for a cameo on "The Walking Dead" as the zombie OS that has risen from the grave.

Now, there is a reason to believe XP use increased, but this is not a sign of a sudden retrograde from Windows 8/8.1 to XP. Remember, Net Applications measures active users, not installed PCs. My belief is that Windows 8 is more widely used in the U.S. and Western Europe, while XP is still predominant in emerging countries, many of which are non-Christian and for whom December was nothing special.

In the west, December was a time of slowdown and vacations for the Christmas break, plus western New Year. A lot fewer people were working in the west, while in places like China and India, where XP is still strong, December 25 was just another day. With all of us in the west back to work, I expect to see a 180 on those numbers.

There are two other metrics to look at the XP numbers. StatCounter shows a minor uptick for XP, from 10.7% in November to 11.9% in December, while Windows 8.1 grew, from 10.9% in November to 11.7% in the same month. Interestingly, StatCounter says Windows 8 has plunged from 7.5% in January 2014 to 4.2% in December, while 8.1 went from 2% in January to 11.7% in December. So it would seem Windows 8.1 did pick up some interest in the maligned OS.

Then there's Steam Analytics. As always, I preface this by noting that Steam is a consumer product (it's iTunes for PC game sales), but it is on a lot of home PCs. It showed Windows 8.1 growing by 2% in December to 25.5% total, and that's an installed base, not used PCs. XP shrank 0.14% to just 3.8%. Steam was the only one to pick up on Windows 10, which it put at 0.32%. So gamers are putting Windows 10 through its paces.

The bottom line is we can't go too crazy over the Net Applications numbers, nor should we.