So far, Windows Server 2003 hasn't had any security bulletins. This is most likely due to the locked-down nature of the operating system upon installation.
However, vulnerabilities within other programs can affect the operational quality of the underlying OS. For example, Microsoft released a security update for Internet Explorer on June 4, 2003. While the corrections made to IE affect all versions of IE since 5.01 on all versions of Windows, Microsoft also released a separate update for WS2K3.
This patch corrects two problems in IE that allow an attacker to run arbitrary code on your server. Download the patch from Microsoft's Web site, and then execute the downloaded program. A reboot is necessary to complete the installation of this hot fix. After your system reboots, open Add/Remove Programs, and select Windows Server 2003 Hotfix - KB 818529.