In case you haven't been paying attention to the news lately, there has been a security flaw publicised that affects Internet Explorer versions 5.01, 6, 6 SP1, and 7. Microsoft even recommends patching IE 8 Beta 2. The flaw could allow remote code execution by visiting compromised websites.

More information can be found on the MS Security Bulletin page for this patch: http://www.microsoft.com/technet/security/bulletin/ms08-078.mspx

It is recommended that everyone install this patch by running Windows Updates. If you have Automatic Updates enabled, you will automatically receive this patch.