Windows Genuine Advantage is a controversy wrapped in an enigma buried inside a migraine headache. Or at least that's what it is for the millions of users who have been falsely identified as software pirates as a result of WGA's attempt to root out piracy.

Since July 2005, one in five computers running Windows have failed so-called Windows Genuine Advantage tests according to data from Microsoft. More than 22 percent of over 500 million systems that were subjected to the browser-based validation scheme were identified as invalid copies of Windows.

All told, some 114 million systems failed the test, which, in terms of retail sales of Windows XP, accounts for over $5 billion in lost potential revenue. The problem with such estimates is that it is unclear why all of these systems failed. Less than 0.5% of these systems were reported as having counterfeit software. Were the rest necessarily pirated by end users? No.

Last summer Microsoft admitted that over 20% of WGA failures were caused by something other than key piracy, that is, piracy involving either a product key generator or use of a volume licensing key. The company would not reveal the exact nature of these results, other than to say that a portion of them stemmed from unauthorized use of OEM keys on non-OEM hardware (i.e., someone using a Dell copy of XP on a non-Dell machine). At the time, Microsoft refused to comment on the rate of pure false positives, that is, the rate of verifiably incorrect identifications of pirated software.

With the release of this latest data, Microsoft said that WGA had a false positive rate "under 1 percent." A more precise number has not been forthcoming.

This is an impressive figure until you realize that this means that as many as 5 million people were wrongly accused of being software pirates. From Microsoft's point of view, the error rate appears to be acceptable. 1 percent sounds pretty low, doesn't it? That slice grows to almost 5 percent if you talk only about false positives as a total share of all "hits" on pirated software.

The concern, of course, is scale. WGA is not in use all over the globe yet, but one can easily see how this 1 percent could bloom into truly astounding numbers. Add to this the fact that Microsoft has big plans for Office Genuine Advantage, and we start to see a world in which being accused of software piracy becomes statistically more probable than winning the Pick 5.

Regardless, Microsoft is touting these numbers as showing the need for Windows Genuine Advantage. There's certainly something to be said for the high numbers of pirated software found via the process, and Microsoft's right to expect to be paid for its products is not in question. The company does risk something of a public relations mess with all of this, however, and it is disheartening to see technology being used once again to "stomp out piracy" with little care for how it treads on the backs of honest folks.