I've seen it done once, on XP, about five years ago. I do not know the specifics. I would not be surprised if there was more than one way to do it.
I have also seen screen savers on MS Windows crash on their own, usually when there's some kind of memory leak or processor-intensive application running. It does not happen often, but it does happen, at least with a few MS Windows releases prior to Vista. I have not had nearly as much professional experience with MS Windows from Vista onwards as with earlier releases, however, so I cannot vouch for the presence of absence of this problem since Vista hit the market.
My question was more hypothetical than specific, anyway. I know that sometimes software is vulnerable to a denial of service in some way, and that a screen saver might be software that could be affected by that. If this allows a way to bypass the need for a password, it could be a security risk.
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