Microsoft have released their Security Bulletin Summary for April 2008 today which contains information and download links to eight patches for various Microsoft operating systems and applications like Microsoft Office and Microsoft Internet Explorer. Five of the eight security patches are patching critical vulnerabilities while three patch important ones. The update is recommended for every user that uses Windows and or Microsoft Office.
All critical vulnerabilities which affect Microsoft Windows, Microsoft Office and Internet Explorer allow Remote Code Execution. The easiest way to patch these security vulnerabilities is by visiting the Windows Update website with Internet Explorer and let a script check the available updates for your system. Please note that you will be asked if you want to install Service Pack 3 Refresh 2 for Windows XP if you use that operating system. My advise would be to not install this version yet and wait for the release version.
All security updates will be displayed and are selected for immediate download and installation. You could follow the link above which leads to the Microsoft website that explains the vulnerabilities and leads to downloads of the patches. This means that you have to make sure to pick the correct downloads for your operating system and software.

Microsoft releases two security patches for Windows
Microsoft Security Updates April 2009