An upcoming security patch from Microsoft will hit sometime in early May, rumored for May 3rd. The patch will block fake SSL certificates that could open users up to spoofing, phishing and more. There was speculation that Microsoft might deliver the patch OTA, but WinRumors has confirmed from Microsoft that it will indeed require Zune desktop software to install. (Mac users will receive the update via the Windows Phone 7 Connector)
Similar the recent NoDo release, users will be prompted via OTA of an impending update.