Not sure if this has been found already, since it was pretty easy to do. All i did was take the 2.60 update eboot, strip out the .psp and .psar file, and change the UPDATER_VER in the .sfo to ten thousand zeros. When i go to my memory stick to view the games, my psp will freeze up for ten seconds and then shut off. This works for 2.00 for sure. Maybe someone with a newer firmware could check this for me. Not sure if this is an overflow or could possibly lead to anything, but its at least another way to freeze up your psp.
I also found that this has to be in the UPDATE folder of the ms or else it simply comes up as corrupt data.
EDIT: The minimum number of zeros it needs is 12, i guess i went a little overboard with 10000 :)