A few times a message has appeared on my screen suddenly telling me that NT AUTHORITY/SYSTEM was going to shut down my PC. All you can do is save your work and basically take it like a man unforunately and let your computer reboot. This is a security flaw in Microsoft Windows, mainly NT/XP/Server. If you see this message you should install Windows updates as soon as possible. There is basically someone out there sending data to your PC causing this to happen. Advisory Warning to all users of the following operating systems: Microsoft Windows NT 4.0 Microsoft Windows NT 4.0 Terminal Services Edition Microsoft Windows 2000 Microsoft Windows XP Microsoft Windows Server 2003 Your Microsoft Operating System may potentially be under attack by HACKER ACTIVITY. The vulnerability attack can fool software into accepting insecure commands that could let intruders steal data, delete files or eavesdrop on e-mails. Due to the seriousness of this vulnerability the Department of Homeland Security and Microsoft encourages system administrators and computer owners to update vulnerable versions of Microsoft Windows operating systems as soon as possible. Our recommendation is to please go to: http://microsoft.com/technet/treeview/default.asp?url=/technet/security/bulletin/MS03-026.asp to install the patch immediately.