This indicates an attempt to exploit a Buffer Overrun vulnerability in Microsoft's Local Security Authority Subsystem Service (LSASS).
LSASS is a Windows security and authentication interface. Due to inadequate boundary checking, an attacker can send a specially crafted message to a target computer to execute arbitrary code.
Microsoft Windows 2000, 2003 and XP.
System Compromise: Remote attackers can gain control of vulnerable systems.
Apply the patch, available from the web site: