This is Microsoft’s first release for Windows 7 [just being optimistic, hopefully there won’t be alot more to come in the future]. This update is supposed to patch a critical Remote Code Execution bug along with two other spoofing related vulnerabilities.
Now available on Windows Update and Microsoft Download Center.
For more details:
http://arstechnica.com/microsoft/news/2009/03/windows-7-beta-gets-its-first-security-update.ars