In the middle of last week Apple released a single security update for their Software Update utility for Windows. The utility was updated to version 2.2 to address a security issue (which was assigned a CVE(defined)) that could have allowed an attacker to control the contents of the information presented to the users of the utility about the updates available.
Full details of this update are available from Apple’s support page for this update. To correct this issue, it will require using the vulnerable version of Software Update one final time to check for updates and install the updated version of Software Update.
If you have iTunes or QuickTime installed on Windows, you will very likely also have Software Update installed (which updates/maintains the above mentioned Apple applications), please ensure that you install the appropriate update as soon as possible to resolve this vulnerability.