ARS Technica writes Microsoft's WGA program now has a third classification for users who set off some, but not all of the program's piracy-detection functionality:
While Microsoft has not responded to requests for comment, it's quite obvious what is going on here: Microsoft has added "not sure" as a way of cutting down on the number of false positives associated with WGA. As many as one in five PCs were failing WGA checks, but this new setting should both reduce this and give Microsoft the chance to investigate further the kinds of things that are landing folks in the "not sure" category.
Although the Windows Genuine Advantage Notification tool is "optional," Microsoft is in the process of pushing out the tool as a "critical" and thus automatic update (affectionately dubbed WGA Notifications 1.7 KB905474). The update has been known about for over a month, but users are just now seeing it show up as a critical update to Windows XP.