bypass screensaver password

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Just curious: Is there a way to bypass a screensaver password for XP
without causing too much disturbance like shutting the system down?
The CDRom autoplay is disabled. Normally when entering password of the
XP screensaver, the wallpaper comes back in the background. If
occasionally you don't get the wallpaper but only the password popup
against some background color, it that a sign that the system has been
tampered?

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