We don’t often blog about security udpates as these are more the specialty of sites like http://www.secunia.com , but this Microsoft update is considered critical because it allows a remote external user access to your system.
The vulnerability has been discovered in the Windows TCP/IP stack as well as in the Microsoft Windows Local Security Authority Subsystem Service (LSASS). A knowledgeable person could use this vulnerability to gain full access to the exploited system.
It is highly advisable to apply the following patches :
http://www.microsoft.com/technet/security/Bulletin/MS08-001.mspx
http://www.microsoft.com/technet/security/Bulletin/MS08-002.mspx