There is a flaw in the way the Windows XP, Windows NT 4.0 and Windows 2000 kernel passes error messages to a debugger. A vulnerability results because an attacker could write a program to exploit this flaw and run code of their choice according to Microsoft. "An attacker could exploit this vulnerability to take any action on the system including deleting data, adding accounts with administrative access, or reconfiguring the system."
Additonally, Microsoft is actively working on a revised patch for Windows XP Service Pack 1 that was originally issued on April 16, 2003. It will re-issue that patch when it has been completed and fully tested.
Find out more at http://www.microsoft.com/technet/security/bulletin/MS03-013.asp