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If the owner is not bad enough to use alphanumeric and upper and
lower case letters, it shouldn't take long to recover.
If the owner is that bad, it will take lots of days, if not, years
or eternity, based on how much physical RAM you have and how fast
your processor is. 
And whether they have spywares and what-nots, not my dai ji. These
kind of softwares are usually dubious, so up to you to decide.