In the past couple of days, Microsoft has released an out-of-cycle patch for all versions of Windows from Win2K onwards.  This is serious – apply the patch immediately.

To quote the bulletin: This security update resolves a privately reported vulnerability in the Server service. The vulnerability could allow remote code execution if an affected system received a specially crafted RPC request. On Microsoft Windows 2000, Windows XP, and Windows Server 2003 systems, an attacker could exploit this vulnerability without authentication to run arbitrary code. It is possible that this vulnerability could be used in the crafting of a wormable exploit. Firewall best practices and standard default firewall configurations can help protect network resources from attacks that originate outside the enterprise perimeter.

In plain English – this means that there is a possibility for a remote attack that DOES NOT REQUIRE any action on the part of the user.  If you’re connected to the Internet, you’re vulnerable.

The bulletin is rated “critical” for all versions up to Server 2003 and “Important” for Vista and Server 2008.

Anyone who has automatic updates turned on has probably already received this patch – make sure it’s applied as soon as possible.  If you don’t have updates turned on, go to the link above and download the patch for your version of Windows (listed at the bottom of the page).