For system administrators or those just interested in computer security, a great resource is the Cyber Security Alert system from US-CERT.
US-CERT formed in September 2003 as a partnership between the Department of Homeland Security and the public and private sectors, intended to coordinate the response to security threats from the Internet. US-CERT is the Federal Incident Management Center for the Federal Government and serves as the focal point for cybersecurity issues.
You can get their Cyber Security Alerts by email or add them to your RSS feed.
Here is an example of a recent Cyber Security Alert, warning of a particular security threat to Microsoft software and what actions to take:
Overview
Microsoft has released updates that address vulnerabilities in Microsoft Windows, Internet Explorer, Word, Excel, SharePoint Server, Visual Basic 6 and related components.
I. Description
As part of the Microsoft Security Bulletin Summary for November 2008, Microsoft released updates to address vulnerabilities that affect Microsoft Windows, Internet Explorer, Word, Excel, SharePoint Server, Visual Basic 6 and other related components.
II. Impact
A remote, unauthenticated attacker could gain elevated privileges, execute arbitrary code or cause a vulnerable application to crash.
III. Solution
Microsoft has provided updates for these vulnerabilities in the Microsoft Security Bulletin Summary for December 2008. The security bulletin describes any known issues related to the updates. Administrators are encouraged to note these issues and test for any potentially adverse effects. Administrators should consider using an automated update distribution system such as Windows Server Update Services (WSUS).