Microsoft recently released a new out-of-band patch (which means its out of their normal release cycle), that fixes a serious exploit in the Internet Explorer browser. This exploit allows a web site to execute code on your computer without your permission. This means if you visit the wrong web site you can have your computer infected with some type of malware.
If you have not patched your system, do it now at Microsoft Update. If you have the Windows Automatic Update feature enabled to download and install the patch, you should have it by now. If you don't have this Automatic Update feature enabled on your computer and want it, the instructions for setting it up are available in this article.
For more information on the patch see the following page.