"Tilt bits are provided in the DDI as the driver’s mechanism for reporting that a hacker is suspected. If at any time the graphics driver determines that something improper has happened, then it can set the appropriate tilt bit—for example, if the hash of an output status message doesn’t match the message. If any tilt bit gets set, then Windows Vista will initiate a full reset of the graphics subsystem, so everything will restart, including re-authentication".
I don't expect you to understand the ramifications of this. They mean a Vista PC is vulnerable to a forced reboot by any process, any virus, any worm, any voltage fluctuation - careful where you put those speakers - that can cause a tilt bit to be set.