Apple has released an update to the iTunes application for Windows which fixes issues that could lead to unexpected application termination or arbitrary code execution. The update is available for Windows 7, Windows Vista, and Windows XP SP2 or later.
(Note that iTunes may have been installed on some Windows computers with a QuickTime installation or update.)
iTunes 10.5 for Mac OS X is installed with the Mac OS 10.7.2 and Security Update 2011-006 updates also released today.
For more information, see http://support.apple.com/kb/HT4981