On the 28th of January Microsoft released an installer that fixes the MHTML vulnerability in IE. The details of this vulnerability are listed here: Advisory Information. This vulnerability impacts all versions of Windows, from XP through to Windows 7 and Server 2008 R2. The installer is in msi format can be run either directly from the browser (this doesn't require a reboot in Windows 7 or Server 2008 R2) or deployed through other application updating mechanisms.
Given the wide footprint of this vulnerability, it is not unreasonable to assume that it will be leveraged by nefarious third parties in an attempt to compromised many computers. The release of this fix isn't an security update as such, but administrators should do their best to patch and deploy any fix that addresses a vulnerability with a footprint as wide as this one. You can obtain the update from the following location: http://support.microsoft.com/kb/2501696