When was the last time you've received an update for anything that doesn't bump the version number, and goes unannounced? Probably not recently. But today, Microsoft pushed an update to their Zune desktop client which, on the surface, appears to have changed nothing.
The update, which popped up for many users today, is still yet to be announced by Microsoft, but does make a few changes under the hood. According to KeyboardP on Twitter, the update brings new versions of the "ZuneWMdu.dll" file, as well as its "related resources." If that means nothing to you, this DLL file is officially the "WindowsMobile Device Updater," so perhaps Microsoft is getting ready for the new version of Windows Phone 7 to drop in the near future.
It's odd that Microsoft would make such a change without stating the purpose of the update, or even bumping the version number, so we'll go ahead and assume that this update is in preparation for the first Windows Phone 7 update, which is due sometime this month.
WPCentral says that the new version of Zune is supposed to support backing up the phone content and applications in preparation for the upcoming update, but we're under the impression this functionality is already built-in and we just haven't seen it in action yet.
If you just can't wait for the update, you can download it manually by going to "Settings" in Zune, then hit "General" and "Check for Updates."