Microsoft released their monthly security bulletin yesterday which listed 11 security bulletins containing a total of 17 patches for operating systems and software like Internet Explorer and Microsoft Office. Six of the eleven security bulletins are critical while the remaining five are considered important.
All critical vulnerabilities have the impact of remote code execution while the impact of the important vulnerabilities can be elevation of privilege, Denial of Service and remote code execution. Downloads are available at Windows Update and as single downloads if you follow the links in the security bulletins.
Information regarding all 11 security bulletins including download links can be found at the security bulletin overview website at Microsoft. Every user should update his system as soon as possible.

Microsoft releases security updates for XP and Vista
Microsoft Security Updates April 2009