Read MoreA serious hole in Windows NT and Windows 2000 allows any user (even "guest") to gain complete control of the machine. This bug -- called a "privilege escalation" vulnerability -- is particularly worrisome, because it does more than open the system to attacks from its own users. It also amplifies the dangers associated with other security holes that Microsoft has dismissed as not being serious. Why? Because an intruder who gains entry to a system as an unprivileged user can obtain administrator privileges and take over.