Together with the update for a critical flaw Microsoft released security updates for Internet Explorer 7 beta and Windows Beta 1 today.
These security updates apply only to the official Internet Explorer 7 Beta 1 and Windows Vista Beta 1 builds (build version 5112 for each). You do not need to install this update if you have already installed one of the more recent Windows Vista builds that are available from the Windows Vista/IE 7 beta downloads page on the Connect site (the latest is build 5231). More specific details on the issue and fix, as well as detailed installation instructions, can be found in the release notes that are included in the downloads for these security updates.
More info over here. The updates are only available to official beta testers.