It is highly recommended to receive automatic notifications whenever Microsoft issues Security Bulletins. For instance, you would already know that this month's Patch Tuesday will include six security updates and only one is critical, where critical means a vulnerability whose exploitation could allow the propagation of an Internet worm without user action. Also, critical is the highest category of the threat ranking system.
The advance notification mechanism is intended to help our customers plan for effective deployment of security updates, and includes information about the number of new security updates being released, the software affected, severity levels of vulnerabilities, and information about any detection tools relevant to the updates.
To get notifications in RSS, mobile device, or e-mail format go here - http://technet.microsoft.com/en-us/security/dd252948.aspx